What is DiVicenzo Criteria ?

What are the DiVicenzo criteria? 

The DiVincenzo Criteria (find the paper here) are a set of fundamental requirements formulated by physicist David DiVincenzo in 2000 that define the necessary conditions for building a functional quantum computer.  

The Five Essential DiVincenzo Criteria: 

1. Well-defined qubits: A scalable physical system with well-characterized qubits. The quantum system must have clearly identifiable qubits with known physical parameters. 

2. Qubit initialization: The ability to initialize the state of the qubits to a simple reference state, such as |000…⟩. This provides a clear starting point for quantum algorithms. 

3. Long coherence times: Quantum coherence times (see article [coherence]) substantially longer than gate operation times. Qubits must maintain their quantum state long enough to complete calculations before decoherence occurs. 

4. Universal gate set: A “universal” set of quantum gates that can implement any quantum algorithm through their combinations. 

5. Qubit-specific measurement: The ability to measure specific qubits without disturbing others, providing reliable readout of computational results. 

Additional Criteria for Quantum Communication: 

6. Interconversion between stationary and flying qubits: The ability to convert between qubits used for computation and qubits used for transmitting quantum information. 

7. Faithful transmission of flying qubits: The ability to transmit qubits between specific locations with high fidelity. 

Photonic Quantum Computing and the DiVincenzo Criteria: 

In photonic quantum computing, these criteria are addressed as follows: 

1. Well-defined qubits: Photonic qubits can be encoded using various degrees of freedom such as polarization, path, time-bin, or frequency. In path encoding, a photon in the upper mode |10⟩⟩ or the lower mode |01⟩⟩ represent the qubit states|0⟩ and |1⟩ respectively. 

2. Qubit initialization: Single-photon sources combined with a spatial demultiplexer can generate well-defined path- encoded qubits. 

3. Long coherence times: Photons naturally have excellent coherence properties as they interact weakly with their environment. In free space or optical fibers, photons can maintain coherence over long distances, though losses can occur. 

4. Universal gate set: Linear optical elements like beam splitters, and tunable phase shifters can implement arbitrary single-qubit operations. Two-qubit gates can be implemented through quantum interference effects and ancillary photons, as in the Knill-Laflamme-Milburn (KLM) protocol (see article [KLM]). 

5. Qubit-specific measurement: Photonic qubits can be measured using superconducting nanowire single-photon detectors. 

6. Interconversion capability: Photons naturally serve as flying qubits, making photonic systems particularly well-suited for quantum communication networks. 

7. Faithful transmission: Photons can be transmitted through optical fibers or free space with relatively low decoherence, though losses must be managed through quantum repeaters for long-distance communication. 

Frequently Asked Questions About the DiVincenzo Criteria 

1. Why are the DiVincenzo Criteria important? These criteria provide a concrete framework for evaluating the viability of different quantum computing technologies and help researchers focus on overcoming specific technical challenges. 

2. Which quantum computing platform satisfied the DiVincenzo Criteria? As of now, significant progress has been made across multiple platforms. The leading technologies are superconducting, trapped ions, photonic, neutral atoms. 

3. Are the DiVincenzo Criteria sufficient for practical quantum computing? While necessary, these criteria don’t address all considerations for practical quantum computing, such as scalability challenges, error correction overhead, and system integration.