PUBLICATIONS
Discover the work of our talented researchers
"It's by logic that we prove, but by intuition that we discover " – Henri Poincaré
+
40
PhDs
2762
Citations
65
Publications
8
Research teams
Indistinguishability of remote quantum dot-cavity single-photon sources
×
Generating identical photons from remote emitter-based bright single-photon sources is an important step for scaling up optical quantum technologies. Here, we study the Hong-Ou-Mandel interference of photons emitted from remote sources based on semiconductor quantum dots. We make use of a deterministic fabrication technique to position the quantum dots in a spectrally resonant micropillar cavity and fine tune their operation wavelength electrically. Doing so, we can match four pairs of sources between five distinct sources, study them under various excitation schemes and measure their degree of indistinguishability. We demonstrate remote indistinguishabiltiy between 44±1% and 69±1% depending on the pair of sources and excitation conditions, record values for quantum dots in cavities. The relative contribution of pure dephasing and spectral diffusion is then analysed, revealing that the remaining distinguishability is mostly due to low frequency noise
Minimizing resource overhead in fusion-based quantum computation using hybrid spin-photon devices
×
Cited by 1
We present three schemes for constructing a (2,2)-Shor-encoded 6-ring photonic resource state for fusion-based quantum computing, each relying on a different type of photon source. We benchmark these architectures by analyzing their ability to achieve the best-known loss tolerance threshold for fusion-based quantum computation using the target resource state. More precisely, we estimate their minimum hardware requirements for fault-tolerant quantum computation in terms of the number of photon sources to achieve on-demand generation of resource states with a desired generation period. Notably, we find that a group of 12 deterministic single-photon sources containing a single matter qubit degree of freedom can produce the target resource state near-deterministically by exploiting entangling gates that are repeated until success. The approach is fully modular, eliminates the need for lossy large-scale multiplexing, and reduces the overhead for resource-state generation by several orders of magnitude compared to architectures using heralded single-photon sources and probabilistic linear-optical entangling gates. Our work shows that the use of deterministic single-photon sources embedding a qubit substantially shortens the path toward fault-tolerant photonic quantum computation.
READ IT ON OPTICA
2024-11-13
Quantum interferences and gates with emitter-based coherent photon sources
Cited by 2
Quantum interferences and gates with emitter-based coherent photon sources
×
Cited by 2
Quantum emitters such as quantum dots, defects in diamond or in silicon have emerged as efficient single photon sources that are progressively exploited in quantum technologies. In 2019, it was shown that the emitted single photon states often include coherence with the vacuum component. Here we investigate how such photon-number coherence alters quantum interference experiments that are routinely implemented both for characterising or exploiting the generated photons. We show that it strongly modifies intensity correlation measurements in a Hong-Ou-Mandel experiment and leads to errors in indistinguishability estimations. It also results in additional entanglement when performing partial measurements. We illustrate the impact on quantum protocols by evidencing modifications in heralding efficiency and fidelity of two-qubit gates.
Quantum circuit compression using qubit logic on qudits
×
We present qubit logic on qudits (QLOQ), a compression scheme in which the qubits from a hardware agnostic circuit are divided into groups of various sizes, and each group is mapped to a physical qudit for computation. QLOQ circuits have qubit-logic inputs, outputs, and gates, making them compatible with existing qubit-based algorithms and Hamiltonians. We show that arbitrary qubit-logic unitaries can in principle be implemented with significantly fewer two-level (qubit) physical entangling gates in QLOQ than in qubit encoding. We achieve this advantage in practice for two applications: variational quantum algorithms, and unitary decomposition. The variational quantum eigensolver (VQE) for LiH took 5 hours using QLOQ on one of Quandela’s cloud-accessible photonic quantum computers, whereas it would have taken 4.39 years in qubit encoding. We also provide a QLOQ version of the Quantum Shannon Decomposition, which not only outperforms previous qudit-based proposals, but also beats the theoretical lower bound on the CNOT cost of unitary decomposition in qubit encoding.
Comparing the performance of practical two-qubit gates for individual Yb ions in yttrium orthovanadate
×
In this paper, we investigate three schemes for implementing Controlled-NOT (CNOT) gates between individual ytterbium (Yb) rare-earth ions doped into yttrium orthovanadate (YVO4 or YVO). Specifically, we investigate the CNOT gates based on magnetic dipolar interactions between Yb ions, photon scattering off a cavity, and a photon interference-based protocol, with and without an optical cavity. We introduce a theoretical framework for precise computations of gate infidelity, accounting for noise effects. We then compute the gate fidelity of each scheme to evaluate the feasibility of their experimental implementation. Based on these results, we compare the performance of the gate schemes and discuss their respective advantages and disadvantages. We conclude that the probabilistic photon interference-based scheme offers the best fidelity scaling with cooperativity and is superior with the current technology of Yb values, while photon scattering is nearly deterministic but slower with less favourable fidelity scaling as a function of cooperativity. The cavityless magnetic dipolar scheme provides a fast, deterministic gate with high fidelity if close ion localization can be realized.
Deterministic and reconfigurable graph state generation with a single solid-state quantum emitter
×
Cited by 2
Measurement-based quantum computing offers a promising route towards scalable, universal photonic quantum computation. This approach relies on the deterministic and efficient generation of photonic graph states in which many photons are mutually entangled with various topologies. Recently, deterministic sources of graph states have been demonstrated with quantum emitters in both the optical and microwave domains. In this work, we demonstrate deterministic and reconfigurable graph state generation with optical solid-state integrated quantum emitters. Specifically, we use a single semiconductor quantum dot in a cavity to generate caterpillar graph states, the most general type of graph state that can be produced with a single emitter. By using fast detuned optical pulses, we achieve full control over the spin state, enabling us to vary the entanglement topology at will. We perform quantum state tomography of two successive photons, measuring Bell state fidelities up to 0.80±0.04 and concurrences up to 0.69±0.09, while maintaining high photon indistinguishability. This simple optical scheme, compatible with commercially available quantum dot-based single photon sources, brings us a step closer to fault-tolerant quantum computing with spins and photons.
Efficient fiber-pigtailed source of indistinguishable single photons
×
Cited by 2
Semiconductor quantum dots in microcavities are an excellent platform for the efficient generation of indistinguishable single photons. However, their use in a wide range of quantum technologies requires their controlled fabrication and integration in compact closed-cycle cryocoolers, with a key challenge being the efficient and stable extraction of the single photons into a single-mode fiber. Here we report on a novel method for fiber-pigtailing of deterministically fabricated single-photon sources. Our technique allows for nanometer-scale alignment accuracy between the source and a fiber, alignment that persists all the way from room temperature to 2.4 K. We demonstrate high performance of the device under near-resonant optical excitation with g(2)(0) = 1.3 %, a photon indistinguishability of 97.5 % and a fibered brightness of 20.8 %. We show that the indistinguishability and single-photon rate are stable for over ten hours of continuous operation in a single cooldown. We further confirm that the device performance is not degraded by nine successive cooldown-warmup cycles.
On the role of coherence for quantum computational advantage
×
Quantifying the resources available to a quantum computer appears to be necessary to separate quantum from classical computation. Among them, entanglement, magic and coherence are arguably of great significance. We introduce path coherence as a measure of the coherent paths interferences arising in a quantum computation. Leveraging the sum-over-paths formalism, we obtain a classical algorithm for estimating quantum transition amplitudes, the complexity of which scales with path coherence. As path coherence relates to the hardness of classical simulation, it provides a new perspective on the role of coherence in quantum computational advantage. Beyond their fundamental significance, our results have practical applications for simulating large classes of quantum computations with classical computers.
Enhanced Fault-tolerance in Photonic Quantum Computing: Floquet Code Outperforms Surface Code in Tailored Architecture
×
Cited by 5
Fault-tolerant quantum computing is crucial for realizing large-scale quantum computation, and the interplay between hardware architecture and quantum error-correcting codes is a key consideration. We present a comparative study of two quantum error-correcting codes – the surface code and the honeycomb Floquet code – implemented on variants of the spin-optical quantum computing architecture, enabling a direct comparison of the codes using consistent noise models. Our results demonstrate that the honeycomb Floquet code significantly outperforms the surface code in this setting. Notably, we achieve a photon loss threshold of 6.4% for the honeycomb Floquet code implementation – to our knowledge the highest reported for photonic platforms to date without large-scale multiplexing. This finding is particularly significant given that photon loss is the primary source of errors in photon-mediated quantum computing.
A deterministic and efficient source of frequency-polarization hyper-encoded photonic qubits
×
Cited by 1
The frequency or color of photons is an attractive degree of freedom to encode and distribute the quantum information over long distances. However, the generation of frequency-encoded photonic qubits has so far relied on probabilistic non-linear single-photon sources and inefficient gates. Here, we demonstrate the deterministic generation of photonic qubits hyper-encoded in frequency and polarization based on a semiconductor quantum dot in a cavity. We exploit the double dipole structure of a neutral exciton and demonstrate the generation of any quantum superposition in amplitude and phase, controlled by the polarization of the pump laser pulse. The source generates frequency-polarization single-photon qubits at a rate of 4 MHz corresponding to a generation probability at the first lens of 28 ± 2%, with a photon number purity > 98%. The photons show an indistinguishability > 91% for each dipole and 88% for a balanced quantum superposition of both. The density matrix of the hyper-encoded photonic state is measured by time-resolved polarization tomography, evidencing a fidelity to the target state of 94 ± 8% and concurrence of 77 ± 2%, here limited by frequency overlap in our device. Our approach brings the advantages of quantum dot sources to the field of quantum information processing based on frequency encoding.
A photonic parameter-shift rule: enabling gradient computation for photonic quantum computers
×
We present a method for gradient computation in quantum algorithms implemented on linear optical quantum computing platforms. While parameter-shift rules have become a staple in qubit gate-based quantum computing for calculating gradients, their direct application to photonic platforms has been hindered by the non-unitary nature of differentiated phase-shift operators in Fock space. We introduce a photonic parameter-shift rule that overcomes this limitation, providing an exact formula for gradient computation in linear optical quantum processors. Our method scales linearly with the number of input photons and utilizes the same parameterized photonic circuit with shifted parameters for each evaluation. This advancement bridges a crucial gap in photonic quantum computing, enabling efficient gradient-based optimization for variational quantum algorithms on near-term photonic quantum processors. We demonstrate the efficacy of our approach through numerical simulations in quantum chemistry and generative modeling tasks, showing superior optimization performance as well as robustness to noise from finite sampling and photon distinguishability compared to other gradient-based and gradient-free methods.
Towards quantum advantage with photonic state injection
×
Cited by 1
We propose a new scheme for near-term photonic quantum device that allows to increase the expressive power of the quantum models beyond what linear optics can do. This scheme relies upon state injection, a measurement-based technique that can produce states that are more controllable, and solve learning tasks that are not believed to be tackled classically. We explain how circuits made of linear optical architectures separated by state injections are keen for experimental implementation. In addition, we give theoretical results on the evolution of the purity of the resulting states, and we discuss how it impacts the distinguishability of the circuit outputs. Finally, we study a computational subroutines of learning algorithms named probability estimation, and we show the state injection scheme we propose may offer a potential quantum advantage in a regime that can be more easily achieved that state-of-the-art adaptive techniques. Our analysis offers new possibilities for near-term advantage that require to tackle fewer experimental difficulties.
Towards practical secure delegated quantum computing with semi-classical light
×
Secure Delegated Quantum Computation (SDQC) protocols are a vital piece of the future quantum information processing global architecture since they allow end-users to perform their valuable computations on remote quantum servers without fear that a malicious quantum service provider or an eavesdropper might acquire some information about their data or algorithm. They also allow end-users to check that their computation has been performed as they have specified it. However, existing protocols all have drawbacks that limit their usage in the real world. Most require the client to either operate a single-qubit source or perform single-qubit measurements, thus requiring them to still have some quantum technological capabilities albeit restricted, or require the server to perform operations which are hard to implement on real hardware (e.g isolate single photons from laser pulses and polarisation-preserving photon-number quantum non-demolition measurements). Others remove the need for quantum communications entirely but this comes at a cost in terms of security guarantees and memory overhead on the server’s side. We present an SDQC protocol which drastically reduces the technological requirements of both the client and the server while providing information-theoretic composable security. More precisely, the client only manipulates an attenuated laser pulse, while the server only handles interacting quantum emitters with a structure capable of generating spin-photon entanglement. The quantum emitter acts as both a converter from coherent laser pulses to polarisation-encoded qubits and an entanglement generator. Such devices have recently been used to demonstrate the largest entangled photonic state to date, thus hinting at the readiness of our protocol for experimental implementations.
Entanglement-enhanced Quantum Reinforcement Learning: an Application using Single-Photons
×
Cited by 1
Quantum Reinforcement Learning (QRL) is an emerging field with many novel approaches suitable for noisy intermediate-scale quantum (NISQ) devices being proposed recently. Projective Simulation (PS) is a classical machine learning method based on random walks in a Directed Acyclic Graph (DAG), and is mainly used to train agents in a Reinforcement Learning setup. This graph corresponds to the Episodic Compositional Memory (ECM) of the agent. For the quantum version of PS we use quantum walks of single photons in quantum optical circuits, which go through tunable components (beamsplitters and phase shifters). We call this specific model Quantum Optical Projective Simulation (QOPS). In this work, we propose a general framework to translate any 2-layer ECM to a quantum optical circuit and an algorithm for solving quantum strategic games using QOPS. Moreover, we introduce QOPS with an entangled state as input. The application that we are using to evaluate the performance of the framework is the Prisoner’s Dilemma. We executed the implementation using Altair’s noisy simulator, designed to emulate a single photon-based quantum processor by Quandela. The algorithm provided promising results even in the presence of noise, which makes it a strong candidate for runs on single-photon-based quantum processors.
Connecting quantum circuit amplitudes and matrix permanents through polynomials
×
In this paper, we strengthen the connection between qubit-based quantum circuits and photonic quantum computation. Within the framework of circuit-based quantum computation, the sum-over-paths interpretation of quantum probability amplitudes leads to the emergence of sums of exponentiated polynomials. In contrast, the matrix permanent is a combinatorial object that plays a crucial role in photonic by describing the probability amplitudes of linear optical computations. To connect the two, we introduce a general method to encode an F2-valued polynomial with complex coefficients into a graph, such that the permanent of the resulting graph’s adjacency matrix corresponds directly to the amplitude associated the polynomial in the sum-over-path framework. This connection allows one to express quantum amplitudes arising from qubit-based circuits as permanents, which can naturally be estimated on a photonic quantum device.
Towards Photon-Number-Encoded High-dimensional Entanglement from a Sequentially Excited Quantum Three-Level System
×
The sequential resonant excitation of a 2-level quantum system results in the emission of a state of light showing time-entanglement encoded in the photon-number-basis – notions that can be extended to 3-level quantum systems as discussed in a recent proposal. Here, we report the experimental implementation of a sequential two-photon resonant excitation process of a solid-state 3-level system, constituted by the biexciton-, exciton-, and ground-state of a semiconductor quantum dot. The resulting light state exhibits entanglement in time and energy, encoded in the photon-number basis, which could be used in quantum information applications, e.g., dense information encoding or quantum communication protocols. Performing energy- and time-resolved correlation experiments in combination with extensive theoretical modelling, we are able to partially retrieve the entanglement structure of the generated state.
High-fidelity four-photon GHZ states on chip
×
Cited by 9
Mutually entangled multi-photon states are at the heart of all-optical quantum technologies. While impressive progresses have been reported in the generation of such quantum light states using free space apparatus, high-fidelity high-rate on-chip entanglement generation is crucial for future scalability. In this work, we use a bright quantum-dot based single-photon source to demonstrate the high fidelity generation of 4-photon Greenberg-Horne-Zeilinger (GHZ) states with a low-loss reconfigurable glass photonic circuit. We reconstruct the density matrix of the generated states using full quantum-state tomography reaching an experimental fidelity to the target state of , and a purity of . The entanglement of the generated states is certified with a semi device-independent approach through the violation of a Bell-like inequality by more than 39 standard deviations. Finally, we carry out a four-partite quantum secret sharing protocol on-chip where a regulator shares with three interlocutors a sifted key with up to 1978 bits, achieving a qubit-error rate of 10.87%. These results establish that the quantum-dot technology combined with glass photonic circuitry offers a viable path for entanglement generation and distribution.
Photonic quantum generative adversarial networks for classical data
×
In generative learning, models are trained to produce new samples that follow the distribution of the target data. These models were historically difficult to train, until proposals such as Generative Adversarial Networks (GANs) emerged, where a generative and a discriminative model compete against each other in a minimax game. Quantum versions of the algorithm were since designed, both for the generation of classical and quantum data. While most work so far has focused on qubit-based architectures, in this article we present a quantum GAN based on linear optical circuits and Fock-space encoding, which makes it compatible with near-term photonic quantum computing. We demonstrate that the model can learn to generate images by training the model end-to-end experimentally on a single-photon quantum processor.
Mitigating photon loss in linear optical quantum circuits: classical post processing methods outperforming post selection
×
Cited by 3
We develop classical postprocessing techniques to mitigate the effects of photon loss, and show that these outperform existing strategies of dealing with loss such as post-selection. Our approach significantly enhances the performance of photonic quantum systems by addressing one of the key challenges in photonic quantum computing. We demonstrate how these techniques can be applied to various photonic quantum algorithms, improving their robustness and reliability in practical implementations.
An error-mitigated photonic quantum circuit Born machine
×
Cited by 1
We introduce a photonic version of a quantum circuit Born machine, a type of quantum generative model, and show that applying our newly developed photon loss mitigation technique allows recovering trainability of this model in realistic lossy scenarios. Our work advances photonic quantum machine learning capabilities by addressing the critical challenge of photon loss. We demonstrate the effectiveness of our approach in enhancing the performance and practical applicability of quantum generative models on photonic platforms.
Simple rules for two-photon state preparation with linear optics
×
Cited by 1
We derive necessary and sufficient conditions for two-photon entanglement in linear optics. We characterize input states for arbitrary two-qudit preparation in d-rail encoding and determine auxiliary photon requirements for heralded two-photon state preparation. We present a construction for generalized post-selected n-qubit control-rotation gates. Our findings advance probabilistic entanglement methods for quantum communication and computation, enhancing the toolkit for photonic quantum information processing.
Faster and shorter synthesis of Hamiltonian simulation circuits
×
Cited by 2
We develop greedy heuristics for quantum circuit synthesis of Pauli rotations, optimizing for minimal entangling gate count or depth with flexible rotation ordering options. Our benchmarks show up to 4x depth reduction compared to state-of-the-art Hamiltonian simulation circuits. This approach is applicable to generic quantum circuit optimization via decomposition and resynthesis, advancing quantum circuit design efficiency.
Verification of Quantum Computations without Trusted Preparations or Measurements
×
Cited by 5
We introduce novel quantum verification protocols. Our first protocol reduces BQP verification to trusted Z-axis rotations and bit flips. The second enables verification of arbitrary quantum computations without trusted preparations or measurements, achieving information-theoretic security. This protocol requires the verifier to perform multi-qubit gates on a size-independent register. We advance Secure Delegated Quantum Computing, settling the open question on universal quantum computation verification with a modular, composable, and efficient approach to transform existing schemes.
Four-photon GHZ states generated on a laser written integrated platform
×
We present an experiment where a reconfigurable photonic processor fabricated in glass by femtosecond laser micromachining is used for the generation of four-photons GHZ entangled states, with high efficiency and fidelity. The chip is used in synergy with a bright and quasi-deterministic source of single photons based on semiconductor quantum dot. The very efficient interfacing of these two platforms is ensured by the excellent connectivity between glass photonic circuits and standard optical fibers. In addition, in order to benchmark the quality of the generated states, this processor is used to implement a quantum secret sharing protocol on chip.
Quantum bounds for compiled XOR games and d-outcome CHSH games
×
Cited by 3
Nonlocal games play a crucial role in quantum information theory and have numerous applications in certification and cryptographic protocols. Kalai et al. (STOC 2023) introduced a procedure to compile a nonlocal game into a single-prover interactive proof, using a quantum homomorphic encryption scheme, and showed that their compilation method preserves the classical bound of the game. Natarajan and Zhang (FOCS 2023) then showed that the quantum bound is preserved for the specific case of the CHSH game. Extending the proof techniques of Natarajan and Zhang, we show that the compilation procedure of Kalai et al. preserves the quantum bound for two classes of games: XOR games and d-outcome CHSH games. We also establish that, for any pair of qubit measurements, there exists an XOR game such that its optimal winning probability serves as a self-test for that particular pair of measurements.
A Complete Graphical Language for Linear Optical Circuits with Finite-Photon-Number Sources and Detectors
×
Cited by 2
Linear optical circuits can be used to manipulate the quantum states of photons as they pass through components including beam splitters and phase shifters. Those photonic states possess a particularly high level of expressiveness, as they reside within the bosonic Fock space, an infinite-dimensional Hilbert space. However, in the domain of linear optical quantum computation, these basic components may not be sufficient to efficiently perform all computations of interest, such as universal quantum computation. To address this limitation it is common to add auxiliary sources and detectors, which enable projections onto auxiliary photonic states and thus increase the versatility of the processes. In this paper, we introduce the LOfi-calculus, a graphical language to reason on the infinite-dimensional bosonic Fock space with circuits composed of four core elements of linear optics: the phase shifter, the beam splitter, and auxiliary sources and detectors with bounded photon number. We present an equational theory that we prove to be complete: two LOfi-circuits represent the same quantum process if and only if one can be transformed into the other with the rules of the LOfi-calculus. We give a unique and compact universal form for such circuits.
Spin Noise Spectroscopy of a Single Spin using Single Detected Photons
×
Cited by 3
Spin noise spectroscopy has become a widespread technique to extract information on spin dynamics in atomic and solid-state systems, in a potentially non-invasive way, through the optical probing of spin fluctuations. Here we experimentally demonstrate a new approach in spin noise spectroscopy, based on the detection of single photons. Due to the large spin-dependent polarization rotations provided by a deterministically-coupled quantum dot-micropillar device, giant spin noise signals induced by a single-hole spin are extracted in the form of photon-photon cross-correlations. Ultimately, such a technique can be extended to an ultrafast regime probing mechanisms down to few tens of picoseconds.
Solid‐State Single‐Photon Sources: Recent Advances for Novel Quantum Materials
×
Cited by 25
In this review, we describe the current landscape of emergent quantum materials for quantum photonic applications. We focus on three specific solid-state platforms: single emitters in monolayers of transition metal dichalcogenides, defects in hexagonal boron nitride, and colloidal quantum dots in perovskites. These platforms share a unique technological accessibility, enabling the rapid implementation of testbed quantum applications, all while being on the verge of becoming technologically mature enough for a first generation of real-world quantum applications. The review begins with a comprehensive overview of the current state-of-the-art for relevant single-photon sources in the solid-state, introducing the most important performance criteria and experimental characterization techniques along the way. We then benchmark progress for each of the three novel materials against more established (yet complex) platforms, highlighting performance, material-specific advantages, and giving an outlook on quantum applications. This review will thus provide the reader with a snapshot on latest developments in the fast-paced field of emergent single-photon sources in the solid-state, including all the required concepts and experiments relevant to this technology.
Photonic quantum interference in the presence of coherence with vacuum
×
Cited by 2
We study the impact of coherence with vacuum in photonic states emitted by quantum emitters such as atoms or quantum dots. We examine how this superposition of vacuum and one-photon components affects photonic quantum information processing. Our investigation begins with Hong-Ou-Mandel (HOM) interference, a fundamental process in quantum photonic technology. We analyze the implications of this coherence on the performance and fidelity of quantum operations, providing insights into the challenges and potential solutions for using these quantum emitters in practical quantum information applications
A Spin-Optical Quantum Computing Architecture
×
Cited by 13
We have developed a novel fault-tolerant quantum computing architecture called Spin-Optical Quantum Computing (SPOQC). Fault-tolerant quantum computers, which actively correct errors, are essential for unlocking the full potential of quantum algorithms. This enables us to perform the most challenging quantum computations and surpass the capabilities of classical computers. Our SPOQC architecture combines the advantages of spin qubits and optical systems to achieve robust error correction and scalability, paving the way for practical, large-scale quantum computing.
Corrected Bell and Noncontextuality Inequalities for Realistic Experiments
×
Cited by 9
We quantify and enhance the robustness of quantum contextuality. We propose measures for non-signaling/non-disturbance and measurement sharpness, and prove the continuity of contextual fraction. We establish bounds for assumption relaxations and introduce the notion of genuine contextuality resistant to experimental imperfections. Our findings apply to various existing results and experimental setups, advancing the understanding and practical application of contextuality in quantum information science.
Scalable machine learning-assisted clear-box characterization for optimally controlled photonic circuits
×
Cited by 9
Machine learning-assisted method developed for photonic chip characterization. Scalable, iterative approach using virtual chip replica. Sample-efficient process requires only CW laser and powermeters. Estimates passive phases, crosstalk, beamsplitter reflectivity, relative I/O losses. Enables imperfection mitigation for enhanced device control. Validated on 12-mode Clements-interferometer with 126 phase shifters. Achieves 99.77% average amplitude fidelity for 100 Haar-random unitaries. Advances photonic integrated circuit performance for classical and quantum applications.
One nine availability of a Photonic Quantum Computer on the Cloud toward HPC integration
×
Cited by 2
First cloud-accessible general-purpose single-photon quantum computer introduced. Designed for high availability and HPC environment compatibility. Achieved 92% uptime (one nine availability) over six months. Exceeds availability of most online quantum computing services. Addresses challenges of QC integration in HPC: stability, maintenance, heterogeneity. Advances quantum computing accessibility for hybrid HPC-QC infrastructures. Lays groundwork for real-world problem-solving using combined QC-HPC strengths.
Simulating photon counting from dynamic quantum emitters by exploiting zero-photon measurements
×
Cited by 4
For designing and optimising photonic quantum technologies, numerical simulations are crucial. The Zero Photon Generator is a breakthrough method, which harnesses information from zero-photon measurements, to to give exponential speedup in time-integrated photon-counting simulations.
Quantum error-correcting codes with a covariant encoding
×
Cited by 6
Given some group G of logical gates, for instance the Clifford group, what are the quantum encodings for which these logical gates can be implemented by simple physical operations, described by some physical representation of G? We study this question by constructing a general form of such encoding maps. For instance, we recover that the [[5,1,3]] and Steane codes admit transversal implementations of the binary tetrahedral and binary octahedral groups, respectively. For bosonic encodings, we show how to obtain the GKP and cat qudit encodings by considering the appropriate groups, and essentially the simplest physical implementations. We further illustrate this approach by introducing a 2-mode bosonic code defined from a constellation of 48 coherent states, for which all single-qubit Clifford gates correspond to passive Gaussian unitaries.
A versatile single-photon-based quantum computing platform
×
Cited by 112
We introduce Quandela\’s Ascella quantum processor, a cloud-accessible versatile quantum computing platform based on single photons, and give a comprehensive overview of the software stack, benchmarks, as well as demonstrations of logic gates, algorithms, and building block operations for scalability. Our work showcases the capabilities of this advanced photonic quantum processor, highlighting its potential for both research and practical applications. We provide detailed performance metrics and demonstrate its ability to execute a range of quantum operations and algorithms.
Asymmetric Quantum Secure Multi-Party Computation With Weak Clients Against Dishonest Majority
×
We introduce a novel quantum Secure Multi-Party Computation (SMPC) protocol, lifting classical SMPC to the quantum realm. Our protocol is composably and statistically secure, even with a single honest party, and requires minimal quantum capabilities from clients: single-qubit X-Y plane state preparation. We leverage a new quantum verification technique in our modular construction, uncovering a fundamental invariance in measurement-based quantum computing. This work advances quantum secure multi-party computation capabilities.
Spin-photon entanglement and photonic cluster states generation with a semiconductor quantum dot in a cavity
×
Semiconductor quantum dots have emerged as excellent artificial atoms to both generate and manipulate quantum light. When embedded in cavities, they can generate single photons and entangled photons with unparalleled efficiency and high quantum purity. In this talk, I will discuss how such devices can be used to generate strings of many entangled photons. The method, leveraging the spin-selective optical transition in a charged quantum dot, leads to the generation of indistinguishable photons in linear cluster states or GHZ states at high rates, realizing an important milestone for scaling-up optical quantum technologies.
Linear Optical Logical Bell State Measurements with Optimal Loss-Tolerance Threshold
×
Cited by 12
Quantum threshold theorems impose hard limits on the hardware capabilities to process quantum information. We derive tight and fundamental upper bounds to loss-tolerance thresholds in different linear-optical quantum information processing settings through an adversarial framework, taking into account the intrinsically probabilistic nature of linear optical Bell measurements.
Solving graph problems with single-photons and linear optics
×
Cited by 13
We demonstrate efficient encoding of n×n matrices into 2n-mode linear optical circuits, applying this technique to encode graph information matrices. We propose a photonic quantum processor design incorporating single-photon sources, encoded optical circuits, and single-photon detectors. Our approach solves various graph problems, including bipartite perfect matchings, permanental polynomials, graph isomorphism, and k-densest subgraph. We develop pre-processing methods to boost relevant detection probabilities and validate our findings through numerical simulations. This work advances practical applications for near-term quantum devices in graph theory and combinatorial optimization.
Certified randomness in tight space
×
Cited by 8
Reliable randomness is a core ingredient in algorithms and applications ranging from numerical simulations to sampling and cryptography. The violation of a Bell inequality can certify that intrinsic randomness is being generated, but this certification typically requires spacelike separated devices. In this work, we provide new theoretical tools to certify randomness generation on a small-scale device and perform a first-of-its-kind integrated photonic demonstration combining a quantum dot based single-photon source and a reconfigurable glass chip.
High-fidelity generation of four-photon GHZ states on-chip
×
Cited by 23
We demonstrate high-fidelity on-chip generation and characterization of a 4-photon Greenberger-Horne-Zeilinger (GHZ) state. Our approach combines a bright single-photon source based on a single quantum dot with a reconfigurable, low-loss laser-written photonic chip. This integration of deterministic single-photon emission and advanced photonic circuitry enables the creation of complex multi-photon entangled states with high efficiency. Our work advances the field of integrated quantum photonics, paving the way for scalable quantum information processing and communication applications on chip-scale devices.
Photonic Quantum Computing For Polymer Classification
×
We present a hybrid classical-quantum approach to the binary classification of polymer structures. Two polymer classes visual (VIS) and near-infrared (NIR) are defined based on the size of the polymer gaps. The hybrid approach combines one of the three methods, Gaussian Kernel Method, Quantum-Enhanced Random Kitchen Sinks or Variational Quantum Classifier, implemented by linear quantum photonic circuits (LQPCs), with a classical deep neural network (DNN) feature extractor. The latter extracts from the classical data information about samples chemical structure. It also reduces the data dimensions yielding compact 2-dimensional data vectors that are then fed to the LQPCs. We adopt the photonic-based data-embedding scheme, proposed by Gan et al. [EPJ Quantum Technol. 9, 16 (2022)] to embed the classical 2-dimensional data vectors into the higher-dimensional Fock space. This hybrid classical-quantum strategy permits to obtain accurate noisy intermediate-scale quantum-compatible classifiers by leveraging Fock states with only a few photons. The models obtained using either of the three hybrid methods successfully classified the VIS and NIR polymers. Their accuracy is comparable as measured by their scores ranging from 0.86 to 0.88. These findings demonstrate that our hybrid approach that uses photonic quantum computing captures chemistry and structure-property correlation patterns in real polymer data. They also open up perspectives of employing quantum computing to complex chemical structures when a larger number of logical qubits is available.
High-rate entanglement between a semiconductor spin and indistinguishable photons
×
Cited by 105
We present cluster states of entangled photons represent the main building block for developing error corrected and large scale photonic quantum computers. We demonstrate the generation of three-photon cluster states using a single quantum dot based device, achieving two orders of magnitude with respect to previous state of the art among different quantum technology systems.
Probing the dynamics and coherence of a semiconductor hole spin via acoustic phonon-assisted excitation
×
Cited by 12
Spins in semiconductor quantum dots are promising local quantum memories to generate polarization-encoded photonic cluster states, as proposed in the pioneering Rudolph-Lindner scheme [1]. However, harnessing the polarization degree of freedom of the optical transitions is hindered by resonant excitation schemes that are widely used to obtain high photon indistinguishability. Here we show that acoustic phonon-assisted excitation, a scheme that preserves high indistinguishability, also allows to fully exploit the polarization selective optical transitions to initialise and measure single spin states. We access the coherence of hole spin systems in a low transverse magnetic field and directly monitor the spin Larmor precession both during the radiative emission process of an excited state or in the quantum dot ground state. We report a spin state detection fidelity of 94.7±0.2% granted by the optical selection rules and a 20±5~ns hole spin coherence time, demonstrating the potential of this scheme and system to generate linear cluster states with a dozen of photons
A Complete Equational Theory for Quantum Circuits
×
Cited by 14
In this note, is introduced the first complete equational theory for quantum circuits. More precisely, a set of circuit equations that are proved to be sound and complete: two circuits represent the same quantum evolution if and only if they can be transformed one into the other using the equations.
Strong Simulation of Linear Optical Processes
×
Cited by 19
An algorithm and general framework for the simulation of photons passing through linear optical interferometers.
A Framework for Verifiable Blind Quantum Computation
×
Cited by 3
While it is possible to benchmark devices or use certification techniques under various assumptions, the most stringent proof is given by verification protocols: they provide unconditional assurance that the client will either receive the correct outcome or abort the computation, even against a service provider which actively tries to corrupt the result. We provide the first framework for designing such protocols in a way that both encompasses most known protocols and allows creating new ones in a much simpler way. This streamlines the creation process and allows us to already improve on our previous state-of-the-art protocols for the verification of delegated quantum computation by introducing two new constructions.
Energy-efficient quantum non-demolition measurement with a spin-photon interface
×
Cited by 5
Spin-photon interfaces (SPIs) are key devices of quantum technologies, aimed at coherently transferring quantum information between spin qubits and propagating pulses of polarized light. We study the potential of a SPI for quantum non demolition (QND) measurements of a spin state. After being initialized and scattered by the SPI, the state of a light pulse depends on the spin state. It thus plays the role of a pointer state, information being encoded in the light’s temporal and polarization degrees of freedom. Building on the fully Hamiltonian resolution of the spin-light dynamics, we show that quantum superpositions of zero and single photon states outperform coherent pulses of light, producing pointer states which are more distinguishable with the same photon budget. The energetic advantage provided by quantum pulses over coherent ones is maintained when information on the spin state is extracted at the classical level by performing projective measurements on the light pulses. The proposed schemes are robust against imperfections in state of the art semi-conducting devices.
LOv-Calculus: A Graphical Language for Linear Optical Quantum Circuits
×
Cited by 27
The LOv-calculus, a graphical language for reasoning about linear optical quantum circuits with so-called vacuum state auxiliary inputs.
Quantum Advantage in Information Retrieval
×
Cited by 22
We introduce a related task to random access codes—the Torpedo Game—and show that it admits greater quantum advantage than the comparable random access code. Our work expands the scope of quantum communication advantages, providing new insights into information retrieval tasks. We demonstrate that this novel scenario offers enhanced performance over traditional random access codes, furthering our understanding of quantum communication capabilities.
Perceval: A Software Platform for Discrete Variable Photonic Quantum Computing
×
Cited by 65
We introduce Perceval, an evolutive open-source software platform for simulating and interfacing with discrete variable photonic quantum computers, and describe its main features and components. Our platform provides researchers and developers with powerful tools for photonic quantum computing, offering simulation capabilities and interface options for real quantum systems. We detail the software\’s architecture and highlight its potential for advancing photonic quantum computing research and development.
Assessing the quality of near-term photonic quantum devices
×
Cited by 10
We develop a certification method for photonic quantum devices, tailored for single photon sources, linear optical circuits, and detectors. We use BosonSampling output statistics and introduce the Photonic Quality Factor metric. Our benchmark tests target photon loss and distinguishability, providing evidence for non-classical simulability of passing experiments. We establish scaling requirements for photon loss rate and single-photon state fidelity, highlighting the eventual necessity of error correction for avoiding classical simulability.
Experimental Analysis of Energy Transfers between a Quantum Emitter and Light Fields
×
Cited by 47
Energy transfer between quantum systems can either be achieved through an effective unitary interaction or through the generation of entanglement. This observation defines two types of energy exchange: unitary and correlation energy. Here we propose and implement experimental protocols to access these energy transfers in interactions between a quantum emitter and light fields. Upon spontaneous emission, we measure the unitary energy transfer from the emitter to the optical field and show that it never exceeds half of the total energy and is reduced when introducing decoherence. We then study the interference of the emitted field and a laser field at a beam splitter and show that the energy transfers quantitatively depend on the quantum purity of the emitted field.
Quantifying n-photon indistinguishability with a cyclic integrated interferometer
×
Cited by 37
We report on a universal method to measure the genuine indistinguishability of n-photons – a crucial parameter that determines the accuracy of optical quantum computing. Our approach relies on a low-depth cyclic multiport interferometer with N = 2n modes, leading to a quantum interference fringe whose visibility is a direct measurement of the genuine n-photon indistinguishability. We experimentally demonstrate this technique for a 8-mode integrated interferometer fabricated using femtosecond laser micromachining and four photons from a quantum dot single-photon source. We measure a four-photon indistinguishability up to 0.81±0.03. This value decreases as we intentionally alter the photon pairwise indistinguishability. The low-depth and low-loss multiport interferometer design provides an efficient and scalable path to evaluate the genuine indistinguishability of resource states of increasing photon number.
Contextuality and Wigner Negativity Are Equivalent for Continuous-Variable Quantum Measurements
×
Cited by 39
Equivalence demonstrated between contextuality and Wigner negativity in continuous-variable quantum computing. Unifies previously distinct quantum resources for speedup. Applicable to standard continuous-variable models. Facilitates practical demonstrations of continuous-variable contextuality. Illuminates role of negative probabilities in quantum phase-space representations. Advances understanding of quantum speedup mechanisms in continuous-variable paradigm.
Mitigating errors by quantum verification and post-selection
×
Cited by 13
We introduce a new quantum error mitigation technique based on the accreditation protocol from quantum verification. Our method uses postselection to correct observable expectation values, addressing noise in preparations, gates, and measurements. We provide rigorous error mitigation guarantees under realistic assumptions, tailored for time-dependent behaviors with varying output states. We analyze sample complexity and validate our technique on current quantum hardware, advancing near-term quantum computing capabilities without full QEC overhead.
Photon-number entanglement generated by sequential excitation of a two-level atom
×
Cited by 35
Exploiting the atomic behaviour of a semiconductor quantum dot in a cavity, we develop a novel protocol for the generation of photon number entangled states in the time basis: from a photon number Bell state up to a series of multi-temporal mode entangled states. The results demonstrate the possibility of using single-photon sources to encode quantum information in new ways.
Bright Polarized Single-Photon Source Based on a Linear Dipole
×
Cited by 132
Bright emission of polarized single-photons from quantum dots is demonstrated by taking advantage of phonon-assisted relaxation and the intrinsic linear dipole structure of exciton states. By optical pumping of the exciton state along one of its dipoles we achieve high emission efficiency of indistinguishable photons with linear polarization degree up to 99%, without the need of complex cavity engineering.
Hong-Ou-Mandel Interference with Imperfect Single Photon Sources
×
Cited by 88
Hong-Ou-Mandel interference is a cornerstone of optical quantum technologies. We explore both theoretically and experimentally how the nature of unwanted multi-photon components of single photon sources affect the interference visibility. We apply our approach to quantum dot single photon sources in order to access the mean wavepacket overlap of the single-photon component – an important metric to understand the limitations of current sources. We find that the impact of multi-photon events has thus far been underestimated, and that the effect of pure dephasing is even milder than previously expected.
Sequential generation of linear cluster states from a single photon emitter
×
Cited by 153
We demonstrate single-mode linear cluster state generation using a quantum dot single-photon source and fiber loop entangling gate. Our architecture produces polarization-encoded, individually-addressable photons, achieving up to four-photon linear cluster states. It is programmable for arbitrary photon numbers and employs a resource-efficient approach with a single entangling gate. We advance photonic one-way quantum computing capabilities, utilizing the most efficient single-photon source technology to date.
Generation of non-classical light in a photon-number superposition
×
Cited by 87
Quantum information can be encoded in several degrees of freedom of single photons; we demonstrate the possibility to generate pulses of light containing a superposition of Fock states of different photon number with high quantum purity. By varying the excitation regime we present the deterministic variation of the proportions in between Fock states |0>, |1> and |2>. The results show in this way a new degree of freedom for qubit encoding in quantum computing protocols.
Reproducibility of High-Performance Quantum Dot Single-Photon Sources
×
Cited by 98
Solid-state quantum light emitters are ubiquitous quantum technology devices required for a large plethora of applications. Their integration in complex industrial systems is bounded by the improvement of their efficiency but also by reproducible and high-fidelity fabrication on a large scale. By leveraging the full potential of semiconductor processing and Quandela’s technology, we demonstrate the scalable and reproducible fabrication of a large set of devices with top performances.
Interfacing scalable photonic platforms: solid-state based multi-photon interference in a reconfigurable glass chip
×
Cited by 55
We demonstrate an efficient realization of a modular quantum photonic platform, interconnecting quantum dot single-photon emitters, active demultiplexing, and integrated waveguides on Silica. Our system leverages high brightness and device efficiency, achieving a significant speed-up compared to similar experiments using probabilistic Spontaneous Parametric Down-Conversion (SPDC) and four-wave mixing sources. This work advances the integration of deterministic single-photon sources with photonic circuits, enhancing the performance and scalability of quantum photonic technologies for practical applications in quantum information processing and communication.
Near-optimal single-photon sources in the solid state
×
Cited by 1414
Single-photons are key elements of many future quantum technologies, be it for the realisation of large-scale quantum communication networks1 for quantum simulation of chemical and physical processes or for connecting quantum memories in a quantum computer. Scaling quantum technologies will thus require efficient, on-demand, sources of highly indistinguishable single-photons. Semiconductor quantum dots inserted in photonic structures are ultrabright single photon sources, but the photon indistinguishability is limited by charge noise induced by nearby surfaces. The current state of the art for indistinguishability are parametric down conversion single-photon sources, but they intrinsically generate multiphoton events and hence must be operated at very low brightness to maintain high single photon purity. To date, no technology has proven to be capable of providing a source that simultaneously generates near-unity indistinguishability and pure single-photons with high brightness. Here, we report on such devices made of quantum dots in electrically controlled cavity structures. We demonstrate on-demand, bright and ultra-pure single photon generation. Application of an electrical bias on deterministically fabricated devices is shown to fully cancel charge noise effects. Under resonant excitation, an indistinguishability of 0.9956±0.0045 is evidenced with a g(2)(0)=0.0028±0.0012. The photon extraction of 65% and measured brightness of 0.154±0.015 make this source 20 times brighter than any source of equal quality. This new generation of sources open the way to a new level of complexity and scalability in optical quantum manipulation.
Our research teams
Quandelians are a multidisciplinary, International and talented group of high-performing professionals who approach problems from different perspectives. We think Quandela is a unique place to work. Our team casts a wide net across many locations, lifestyles and backgrounds. Together we create a working environment that feels safe for everyone. We always welcome and respect individuality – reinforcing the importance of a diverse team that is nurtured to grow and evolve.
Research – Algorithms
The Algorithms Team develops, optimizes, and implements cutting-edge quantum algorithms tailored to Quandela’s hardware. They focus on driving applications and innovations in photonic quantum computing, bridging the gap between theoretical potential and practical implementation.
“Photonic quantum algorithms transform the potential of quantum mechanics into actionable insights, unlocking the power of photons to solve intricate challenges and illuminate the way for tomorrow’s quantum breakthroughs.”
Pierre-Emmanuel Emeriau – Head of Algorithms Team
Research – Device Theory
The Device Theory Team enhances device performance through rigorous theoretical models, computational simulations, error mitigation protocols, and benchmarking techniques. They apply advanced mathematics to refine experiments and push the boundaries of quantum device performance.
“Mathematics sharpens our understanding of physics, turning fundamental quantum laws into tools for advancing hardware, refining experiments, and pushing the boundaries of quantum device performance.”
Stephen Wein – Head of Device Theory Team
Research – Scalable Architecture
The Scalable Architecture Team investigates how to arrange and operate Quandela’s pioneering technology to perform large and trustworthy quantum computations. Their areas of expertise include compilation, delegated computing and quantum error correction.
“A good architecture is a bridge between complicated physics and abstract computer science. It orchestrates spins and photons to execute computations for as long as possible and on as many qubits as possible, both in the present pre-fault-tolerant world and in the error-corrected future.”
Boris Bourdoncle – Head of Scalable Architecture Team
Research – Semiconductors
The Research Semiconductors Team focuses on developing innovative approaches to optimize semiconductor single-photon source performance. They explore novel source designs and advanced addressing schemes, aiming to produce high-performance single-photon sources at a large scale for fault-tolerant photonic quantum computing systems.
“Our goal is to pursue new methods for creating large entangled states of photons with high probability and fidelity. As a key part of the joint laboratory formed by Quandela and the C2N, the team also serves as an important connection between Quandela and the academic GOSS group led by Pascale Senellart.”
Sébastien Boissier – Head of Research Semiconductors Team
Quantum Applications
The Quantum Applications Team bridges the gap between industry use-cases, state-of-the-art quantum computing algorithms, and product integration. They develop trust in photonic quantum applications for real-world problems by designing and enhancing cutting-edge algorithms, supporting clients in their quantum transformation journey.
“We support our clients in their quantum transformation. We give classes about photonic quantum computing, identify use-cases in the client’s industry and develop proof-of-concept that then evolve in an in-production algorithm. All those ingredients are crucial for big companies to make their quantum transformation successful.”
Arno Ricou – Head of Quantum Applications Team
Products – Optics, Electronics and QPU Assembling
The Team develops cutting-edge optical systems and optimal control methods for photonic quantum computing. They integrate and assemble these components to create MosaiQ – data center-ready quantum processing units. The team’s work is crucial in advancing the scalability and efficiency of photonic quantum computers.
“The scalability of photonic quantum computers hinges on our ability to manufacture complex opto-electronic systems. As we push the boundaries of photonic integrated circuits fabrication, we’re not just scaling up qubit numbers, but also enhancing the precision and efficiency of quantum operations. The transition to large-scale manufacturing of these intricate systems will be the key to unlocking the full potential of photonic quantum computing.”
Nicolas Maring – Head of Optics, Electronics and QPU assembling Team
Products – Semiconductor Sources Production
The Semiconductor Sources Production team produces one of the world’s brightest quantum single-photon sources using cutting-edge nanofabrication technologies. In each quantum computer, their source serves as the heart, delivering single photons through the fiber channels and circuits of the QPU. Just as there’s no substitute for a heart, their photon source is irreplaceable!
“Competing and embracing yourself every day is the art of making everything better !”
Thi Huong Au – Head of Semiconductor Sources Production Team
Software
The Software Engineer Team develops the quantum computing framework Perceval and manages Quandela’s web and cloud infrastructure. They play a dual role: leading software production with regular Perceval releases and new customer APIs, while also providing internal support to other teams through tool development and code reviews.
“People imagine that driving a quantum computer is something extremely complicated, and this is partly true. In our team, we’re in the business of transforming this into “just” a complex operation, with each element simplified as far as possible. This involves using Python, then sending a computation order via the web to our quantum computers or optimized simulators.”
Mario Valdivia – Head of Software Engineer Team