Quantum photonic devices are typically based on either discrete variable (DV) or continuous variable (CV) principles. In either case, their performance must meet strict “fidelity” requirements, especially when scaled using integrated photonic circuitry. DV devices must be robust to imperfections such as timing delays between photons, unwanted spectral correlations present in photons from nonideal single photon sources and variations in circuit components. Furthermore, it becomes increasingly important to have a methodology for characterizing the performance of devices in the presence of such errors. Here, we present a method for simulating quantum photonic integrated circuits (PICs) and use it to model the behavior of a circuit constructed to model the evolution of a quantum state subject to a Bose-Hubbard Hamiltonian, introducing variations to the coupling gaps in the directional couplers inside the circuit. Input states consisting of both indistinguishable and distinguishable photons are modelled. Compact models for the directional couplers and other photonic circuit elements that are parameterized for a specific fabrication process can be incorporated into the circuit using a foundry-associated compact model library, ensuring consistency between circuit design and manufactured component. In CV applications, the degree of squeezing provided by some nonlinear element is often a key metric. Here we describe how the degree of squeezing produced by spontaneous four-wave mixing (SFWM) in a microring resonator can be modelled in the low-power limit, accounting for the effects of self-phase modulation (SPM), cross-phase modulation (XPM), and component losses.
Discrete variable quantum photonic circuits rely on the interference between indistinguishable photons to produce non-classical results. However, indistinguishability between photons is often spoiled due to timing delays, different spectral profiles, or the presence of unwanted spectral correlations. Additionally, variability in circuit components can introduce further errors. Here we present a method for simulating the frequency domain response of quantum photonic integrated circuits (PICs), allowing the fidelity and probability of success of realistic quantum circuits to be characterized. As an example, we first model the biphoton wavefunction produced by spontaneous four-wave mixing in a silicon nitride microring resonator, then use our methodology to simulate the interference between heralded signal photons from two such sources in the presence of spectral correlations and circuit component variability due to manufacturing imperfections.
The rapidly growing field of integrated photonic quantum computing has recently seen enormous breakthroughs, with integrated photonic devices capable of generating highly entangled states of photons on-chip. To scale these devices, simulation tools that model realistic sources and manufacturing imperfections are required when designing quantum building blocks that meet fidelity requirements and fault tolerance thresholds. To address this, we introduce a quantum circuit solver capable of calculating the heralded source biphoton wavefunction and corresponding frequency domain response of photonic integrated circuits in the Fock basis, yielding the fidelity of the output state and probability of success for a given measurement outcome.
We recently proposed a quantum computing platform that exploits circuit-bound photons to create cluster states and achieve one-way measurement-based quantum computations on arrays of photonically interfaced solid-state spin qubits with long coherence-times. Single photons are used for spin initialization, readout and for photon-mediated long-range entanglement creation. In this conference talk, we elaborate on the challenges that are faced during any practical implementation of this architecture by breaking it down into the key physical building blocks. We further discuss the constraints imposed on the spin qubits and the photonic circuit components that are set by the requirements of achieving fault-tolerant performance.
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