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Quantum Computing, Communication, and Simulation

Simulating quantum photonic processes in realistic photonic integrated circuits: circuit performance analysis using non-classical source-to-detector component parametrization

Sebastian Gitt, Dylan McGuire, Jeff F. Young

Published Mar 8, 2023• 2 citations
Publisher

Abstract

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.

DOI
10.1117/12.2647886

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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.
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.
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.
The capability of realizing quantum photonics implementations on-chip will have a strong impact on several aspects of quantum computation and information processing. The implementation of large scale integrated quantum photonic technologies requires on-chip reconfigurable waveguide circuits as well as single-photon sources and detectors. Many successes have been made in recent years to demonstrate complex quantum circuits in many material platforms. Among all these platforms, the Silicon-on-Insulator (SOI) platform is outstanding as it is well developed for classical applications and therefore deploys a high component density, mature fabrication techniques and compatibility with the telecom regime and the complementary metal-oxide-semiconductor (CMOS) technology. However, the lack of on-demand non-classical light sources, directly incorporated in silicon chips, forces the use of nonlinear processes to generate non-classical light states: the probabilistic nature of the emission process sets a limit in the maximally achievable experimental complexity. The use of on-demand sources will have a strong impact on the device’s scalability.
We introduce the concept and proof-of-principle design of a new type of high-speed photonic integrated analyzers for continuous-variable quantum states. These analyzers aim to address both unconditionally entangled states and noise-squeezed states. Unlike current squeezed state analyzers and entangled state analyzers, our devices do not rely on optical phase-locked loops. Instead, they use a phase-diversity architecture where the local oscillator operates as a free-running laser. This method greatly simplifies system design and allows for photonic integrated circuit realizations that meet the strict size, weight, and power requirements of space-based quantum communication systems. We explain how the integrated analyzers for unconditionally entangled states and noise-squeezed states work, outline their methods for characterizing entanglement and squeezing in the digital domain, and provide a tolerance analysis of the essential photonic components. Numerical modeling shows that our design achieves over 10dB parametric gain with sub-10mW pump powers. It also allows for squeezing levels that exceed the 8dB threshold needed for fault-tolerant continuous-variable quantum computing. This work offers a route to scalable, practical photonic analyzers for quantum communication and information processing applications.
Chip-scale integrated photonic circuits provide an attractive platform for the implementation of many quantum photonic technologies ranging from precise metrology to secure communication and quantum computation. In particular, silicon photonic platforms support micron-scale nonlinear optical sources of non-classical light which can be mass manufactured using the robust fabrication processes pioneered by the CMOS microelectronics industry. Integration of these quantum photonic sources with high-performance classical photonic devices on the same chip is required for truly scalable quantum information technologies. Integrated nonlinear resonators are investigated as sources of quantum mechanically correlated photon pair sources. An all-order dispersion engineering method is presented as a robust design synthesis for micoring sources. In addition, a novel concept of coupled mode dispersion compensation is proposed and demonstrated, providing significantly improved performance characteristics of resonant four-wave mixing sources. Next a photon pair source is demonstrated in a commercial CMOS microelectronics process opening the door to future integration of quantum photonics with electronic logic and control circuits. Classical nonlinear optical measurements of stimulated four-wave mixing are used for the first time to accurately predict the quantum correlations from the same device operating in the photon pair regime. Next the first demonstration of fully on-chip pump rejection is demonstrated with over 95 dB pump extinction improving the figures of merit from previous demonstrations by multiple orders of magnitude, including losses, detected pair rates and size. Finally, proposals for introducing novel degrees of freedom provided by an integrated platform are presented for further improving the performance of both photon pair and classical nonlinear optical sources.
Photonic integrated circuits offer a scalable and robust route toward quantum information technologies by consolidating photon sources and linear optical networks onto compact, wafer-manufacturable chips. Although silicon photonics has enabled diverse discrete-variable quantum breakthroughs -- spanning multiphoton entanglement, quantum networking, and photonic qubit fusion for quantum computing -- scaling these platforms beyond proof-of-principle demonstrations remains severely constrained by a critical system-level bottleneck. Optical loss compounds rapidly across photon generation, routing, and state analysis, causing multiphoton generation probabilities to plummet exponentially as circuit depth and complexity grow. Here we overcome this rate-loss barrier by demonstrating a monolithic, ultralow-loss silicon nitride (Si3_33​N4_44​) integrated photonic platform engineered for high-performance discrete-variable quantum information processing. Our architecture seamlessly integrates narrowband photon-pair sources with low-loss qubit-fusion circuits and reconfigurable state-analysis interferometers. The on-chip sources prepare Einstein-Podolsky-Rosen (EPR) states with a fidelity of 0.9875(3) and exhibit near-unity photon indistinguishability, yielding a heralded Hong-Ou-Mandel interference visibility of 0.990(6). By executing on-chip fusion of two EPR states, we synthesize and characterize four-photon Greenberger-Horne-Zeilinger states with a record fidelity of 0.943(8) and a fourfold count rate of 27 Hz -- more than two orders of magnitude higher than previous silicon-photonic implementations. Combined with standard CMOS-compatible fabrication on 150-mm-diameter wafers, these results establish ultralow-loss Si3_33​N4_44​ integrated photonics as a definitive, manufacturable platform for deployable, large-scale quantum information processors.