A two-qubit gate is an operation that acts on two qubits throughout a quantum computation. Depending on the operation, the qubits, after the application of the two-qubit gate, can be correlated or evolve independently in time. In the evolution of quantum circuits, the presence of two-qubit gates is essential to search for exponentially faster algorithms compared to classical counterparts.
In the case of photons, there are a couple of different ways to create a two photon-gate. One way is through a deterministic process. Firstly, a single photon is generated from an excitation pulse shined on a single-photon source. Then, by repeating the procedure, if we have waited a specific period, we generate the second photon that is entangled with the first one. On the other hand, a probabilistic approach using only linear optics elements is also possible. The creation of this photonic two-qubit gate is heralded depending on the measurement outcomes of the photons.
With Quandela Could, users can simulate and realize quantum circuits with two-qubit gates using a Quantum processor.
Cutting-edge research for two-qubit gates in quantum computation:
- Two-qubit gates, like CNOT, are expensive to be realized. The creation of shallow quantum circuits with a significant reduction in CNOT gates is a branch of quantum information science research.
- Quantum computation with random Haar- based two qubit gates can lead to famous phase transitions by varying the frequency of measurements’ presence in the quantum circuit.
Frequently asked question about two-qubit gates:
- Do all two-qubit gates generate entanglement?
No, for example: a tensor product of two single qubit gates is a two-qubit gate, but it doesn’t create any quantum correlations. A simple way to see if a two-qubit gate can generate quantum correlations is by decomposing it in a well-known basis, like the Pauli Basis.
- Are two-qubit gates stable enough in the different experimental setups?
Unfortunately, a two-qubit gate implementation in a quantum circuit is affected by several parameters. For example, coherence time and unwanted coupling between other states in physical systems can deteriorate the fidelity of a two-qubit gate drastically.