The complexity of experimental quantum information processing devices is increasing rapidly, requiring new approaches to control them. In this paper, we address the problems of practically modeling and controlling an integrated optical waveguide array chip, a technology expected to have many applications in telecommunications and optical quantum information processing. This photonic circuit can be electrically reconfigured, but only the output optical signal can be monitored. As a result, the conventional control methods cannot be naively applied. Characterizing such a chip is challenging for three reasons. First, there are uncertainties associated with the Hamiltonian describing the chip. Second, we expect distortions of the control voltages caused by the chip's electrical response, which cannot be directly observed. Finally, there are imperfections in the measurements caused by losses from coupling the chip externally to optical fibers. We developed a deep neural network approach to solve these problems. The architecture is designed specifically to overcome the aforementioned challenges using a Gated Recurrent Unit (GRU)-based network as the central component. The Hamiltonian is estimated as a blackbox, while the rules of quantum mechanics such as state evolution is embedded in the structure as a whitebox. The resulting overall graybox model of the chip shows good performance both quantitatively in terms of the mean square error and qualitatively in terms of the predicted waveforms. We use this neural network to solve a classical and a quantum control problem. In the classical application we find a control sequence to approximately realize a time-dependent output power distribution. For the quantum application we obtain the control voltages to realize a target set of quantum gates. The proposed method is generic and can be applied to other systems that can only be probed indirectly.
Integrated quantum photonics is an appealing platform for quantum information processing, quantum communication and quantum metrology. In all these applications it is necessary not only to be able to create and detect Fock states of light but also to program the photonic circuits that implements some desired logical operation. Here we demonstrate a reconfigurable controlled two-qubit operation on a chip using a multiwaveguide interferometer with a tunable phase shifter. We find excellent agreement between theory and experiment, with a 0.98 \pm 0.02 average similarity between measured and ideal…
Entanglement is the quintessential quantum mechanical phenomenon understood to lie at the heart of future quantum technologies and the subject of fundamental scientific investigations. Mixture, resulting from noise, is often an unwanted result of interaction with an environment, but is also of fundamental interest, and is proposed to play a role in some biological processes. Here we report an integrated waveguide device that can generate and completely characterize pure two-photon states with any amount of entanglement and arbitrary single-photon states with any amount of mixture. The device c…
Photonic chip based time-bin entanglement has attracted significant attention because of its potential for quantum communication and computation. Useful time-bin entanglement systems must be able to generate, manipulate and analyze entangled photons on a photonic chip for stable, scalable and reconfigurable operation. Here we report the first time-bin entanglement photonic chip that integrates time-bin generation, wavelength demultiplexing and entanglement analysis. A two-photon interference fringe with an 88.4% visibility is measured (without subtracting any noise), indicating the high perfor…
We show that piezoelectric strain actuation of acoustomechanical interactions can produce large phase velocity changes in an existing quantum phononic platform: aluminum nitride on suspended silicon. Using finite element analysis, we demonstrate a piezo-acoustomechanical phase shifter waveguide capable of producing +/- pi phase shifts for GHz frequency phonons in 10s of microns with 10s of volts applied. Then, using the phase shifter as a building block, we demonstrate several phononic integrated circuit elements useful for quantum information processing. In particular, we show how to construc…
The importance of integrated quantum photonics in the telecom band resides on the possibility of interfacing with the optical network infrastructure developed for classical communications. In this framework, femtosecond laser written integrated photonic circuits, already assessed for quantum information experiments in the 800 nm wavelength range, have great potentials. In fact these circuits, written in glass, can be perfectly mode-matched at telecom wavelength to the in/out coupling fibers, which is a key requirement for a low-loss processing node in future quantum optical networks. In additi…
The development of large-scale optical quantum information processing circuits ground on the stability and reconfigurability enabled by integrated photonics. We demonstrate a reconfigurable 8x8 integrated linear optical network based on silicon nitride waveguides for quantum information processing. Our processor implements a novel optical architecture enabling any arbitrary linear transformation and constitutes the largest programmable circuit reported so far on this platform. We validate a variety of photonic quantum information processing primitives, in the form of Hong-Ou-Mandel interferenc…
Reconfigurability of integrated photonic chips plays a key role in current experiments in the area of linear-optical quantum computing. We demonstrate a reconfigurable multiport interferometer implemented as a femtosecond laser-written integrated photonic device. The device includes a femtosecond laser-written $4\times 4$ multiport interferometer equipped with 12 thermooptical phase shifters, making it a universal programmable linear-optical circuit. We achieve a record fast switching time for a single nested Mach-Zender interferometer of $\sim10$ ms and quantitatively analyse the reconfigurab…
We present a modular design for integrated programmable multimode sources of arbitrary Gaussian states of light. The technique is based on current technologies, in particular recent demonstrations of on-chip photon manipulation and generation of highly squeezed vacuum states in semiconductors. While the design is generic and independent of the choice of integrated platform, we adopt recent experimental results on compound semiconductors as a demonstrative example. Such a device would be valuable as a source for many quantum protocols that range from imaging to communication and information pro…
We report a compact, scalable, quantum photonic integrated circuit realised by combining multiple, independent InGaAs/GaAs quantum-light-emitting-diodes (QLEDs) with a silicon oxynitride waveguide circuit. Each waveguide joining the circuit can then be excited by a separate, independently electrically contacted QLED. We show that the emission from neighbouring QLEDs can be independently tuned to degeneracy using the Stark Effect and that the resulting photon streams are indistinguishable. This enables on-chip Hong-Ou-Mandel-type interference, as required for many photonic quantum information p…
Korea Institute of Science and Technology (KIST)（韩国科学技术院）；Korea University（高丽大学）；Seoul National University of Science and Technology（首尔科学技术大学）；Kyung Hee University（庆熙大学）
The development of practical methods for synthesis and verification of complex photonic circuits presents a grand challenge for the nascent field of quantum engineering. Of course, classical electrical engineering provides essential foundations and serves to illustrate the degree of sophistication that can be achieved in automated circuit design. In this paper we explore the utility of term rewriting approaches to the transformation of quantum circuit models, specifically applying rewrite rules for both reduction/verification and robustness analysis of photonic circuits for autonomous quantum …
We study the production of entangled two- and N-mode quantum states of light in optical waveguides. To this end, we propose a quantum photonic circuit that produces a reconfigurable superposition of photon subtraction on two single-mode squeezed states. Under postselection, continuous variable or discrete variable entangled states with possibilities in quantum information processing are obtained. Likewise, nesting leads to higher-dimension entanglement with a similar design, enabling the generation of non-Gaussian continuous variable cluster states. Additionally, we show the operation of the d…
We study the impact of experimental imperfections in integrated photonic circuits. We discuss the emergence of a moderate biased error in path encoding, and investigate its correlation with properties of the optical paths. Our analysis connects and deepens previous studies in this direction, revealing potential issues for high-precision tests and optical implementations of machine learning.
Realizing the advantages of quantum computation requires access to the full Hilbert space of states of many quantum bits (qubits). Thus, large-scale quantum computation faces the challenge of efficiently generating entanglement between many qubits. In systems with a limited number of direct connections between qubits, entanglement between non-nearest neighbor qubits is generated by a series of nearest neighbor gates, which exponentially suppresses the resulting fidelity. Here we propose and demonstrate a novel, on-chip photon exchange network. This photonic network is embedded in a superconduc…
Quantum optical microcombs in integrated ring resonators generate entangled photon pairs over many spectral modes, and allow the preparation of high dimensional qudit states. Ideally, those sources should be programmable and have a high generation rate, with comb lines tightly spaced for the implementation of efficient qudit gates based on electro-optic frequency mixing. While these requirements cannot all be satisfied by a single resonator device, for which there is a trade-off between high generation rate and tight bin spacing, a promising strategy is the use of multiple resonators, each gen…
Scalable photonic quantum technologies are based on multiple nested interferometers. To realize this architecture, integrated optical structures are needed to ensure stable, controllable, and repeatable operation. Here we show a key proof-of-principle demonstration of an externally-controlled photonic quantum circuit based upon UV-written waveguide technology. In particular, we present non-classical interference of photon pairs in a Mach-Zehnder interferometer constructed with X couplers in an integrated optical circuit with a thermo-optic phase shifter in one of the interferometer arms.
Reconfigurable linear optical networks are a key component for the development of optical quantum information processing platforms in the NISQ era and beyond. We report the implementation of such a device based on an innovative design that uses the mode mixing of a multimode fiber in combination with the programmable wavefront shaping of a SLM. The capabilities of the platform are explored in the classical regime. For up to 8 inputs and a record number of 38 outputs, we achieve fidelities in excess of 93%, and losses below 6.5dB. The device was built inside a standard server rack to allow for …
We consider the design of photonic circuits that make use of Ti:LiNbO$_{3}$ diffused channel waveguides for generating photons with various combinations of modal, spectral, and polarization entanglement. Down-converted photon pairs are generated via spontaneous optical parametric down-conversion (SPDC) in a two-mode waveguide. We study a class of photonic circuits comprising: 1) a nonlinear periodically poled two-mode waveguide structure, 2) a set of single-mode and two-mode waveguide-based couplers arranged in such a way that they suitably separate the three photons comprising the SPDC proces…
Quantum metrology takes advantage of nonclassical resources such as entanglement to achieve a sensitivity level below the standard quantum limit. To date, almost all quantum-metrology demonstrations are restricted to improving the measurement performance at a single sensor, but a plethora of applications require multiple sensors that work jointly to tackle distributed sensing problems. Here, we propose and experimentally demonstrate a reconfigurable sensor network empowered by continuous-variable (CV) multipartite entanglement. Our experiment establishes a connection between the entanglement s…
Integrated quantum optics becomes a consequent tendency towards practical quantum information processing. Here, we report the on-chip generation and manipulation of photonic entanglement based on reconfigurable lithium niobate waveguide circuits. By introducing periodically poled structure into the waveguide interferometer, two individual photon-pair sources with controllable phase-shift are produced and cascaded by a quantum interference, resulting in a deterministically separated identical photon pair. The state is characterized by 92.9% visibility Hong-Ou-Mandel interference. Continuous mor…
Reconfigurable quantum photonic processors are an essential technology for photonic quantum computing. Although most large-scale reconfigurable quantum photonic processors were demonstrated at the telecommunications C band around 1550 nm, high-performance single photon light sources utilizing quantum dots that are well-suited for photonic quantum computing operate at a variety of wavelengths. Thus, a demand exists for the compatibility of quantum photonic processors with a larger wavelength range. Silicon nitride (SiN) has a high confinement and wide transparency window, enabling compact, low-…
Devices that achieve nonreciprocal microwave transmission are ubiquitous in radar and radio-frequency communication systems, and commonly rely on magnetically biased ferrite materials. Such devices are also indispensable in the readout chains of superconducting quantum circuits as they protect sensitive quantum systems from the noise emitted by readout electronics. Since ferrite-based nonreciprocal devices are bulky, lossy, and require large magnetic fields, there has been significant interest in magnetic-field-free on-chip alternatives, such as those recently implemented using Josephson junct…
The recent progress in integrated quantum optics has set the stage for the development of an integrated platform for quantum information processing with photons, with potential applications in quantum simulation. Among the different material platforms being investigated, direct-bandgap semiconductors and particularly gallium arsenide (GaAs) offer the widest range of functionalities, including single- and entangled-photon generation by radiative recombination, low-loss routing, electro-optic modulation and single-photon detection. This paper reviews the recent progress in the development of the…
The continual success of superconducting photon-detection technologies in quantum photonics asserts cryogenic-compatible systems as a cornerstone of full quantum photonic integration. Here, we present a way to reversibly fine-tune the optical properties of individual waveguide structures through local changes to their geometry using solidified xenon. Essentially, we remove the need for additional on-chip calibration elements, effectively zeroing the power consumption tied to reconfigurable elements, with virtually no detriment to photonic device performance. We enable passive circuit tuning in…
We demonstrate photonic quantum circuits that operate at the stringent levels that will be required for future quantum information science and technology. These circuits are fabricated from silica-on-silicon waveguides forming directional couplers and interferometers. While our focus is on the operation of quantum circuits, to test this operation required construction of a spectrally tuned photon source to produce near-identical pairs of photons. We show non-classical interference with two photons and a two-photon entangling logic gate that operate with near-unit fidelity. These results are a …
Photonic integrated circuits that are manufactured with mature semiconductor technology hold great promise for realizing scalable quantum technology. Efficient interfaces between quantum emitters and nanophotonic devices are crucial building blocks for such implementations on silicon chips. These interfaces can be realized as nanobeam optical cavities with high quality factors and wavelength-scale mode volumes, thus providing enhanced coupling between nanoscale quantum emitters and nanophotonic circuits. Realizing such resonant structures is particularly challenging for the visible wavelength …
Following the simple observation that the interconnection of a set of quantum optical input-output devices can be specified using structural mode VHSIC Hardware Description Language (VHDL), we demonstrate a computer-aided schematic capture workflow for modeling and simulating multi-component photonic circuits. We describe an algorithm for parsing circuit descriptions to derive quantum equations of motion, illustrate our approach using simple examples based on linear and cavity-nonlinear optical components, and demonstrate a computational approach to hierarchical model reduction.
Using a technique, analogous to coherent population trapping in an atomic system, we propose schemes to create transverse light propagation violating left-right symmetry in a photonic circuit consisting of three coupled waveguides. The frequency windows for the symmetry breaking of the left-right energy flow span over 80 nm. Our proposed system only uses linear passive optical materials and is easy to integrate on a chip.
We report photonic quantum circuits created using an ultrafast laser processing technique that is rapid, requires no lithographic mask and can be used to create three-dimensional networks of waveguide devices. We have characterized directional couplers--the key functional elements of photonic quantum circuits--and found that they perform as well as lithographically produced waveguide devices. We further demonstrate high-performance interferometers and an important multi-photon quantum interference phenomenon for the first time in integrated optics. This direct-write approach will enable the ra…
This paper proposes a machine learning method to characterize photonic states via a simple optical circuit and data processing of photon number distributions, such as photonic patterns. The input states consist of two coherent states used as references and a two-mode unknown state to be studied. We successfully trained supervised learning algorithms that can predict the degree of entanglement in the two-mode state as well as perform the full tomography of one photonic mode, obtaining satisfactory values in the considered regression metrics.
The spectacular success of silicon-based photonic integrated circuits (PICs) in the past decade naturally begs the question of whether similar fabrication procedures can be applied to other material platforms with more desirable optical properties. In this work, we demonstrate the individual passive components (grating couplers, waveguides, multi-mode interferometers and ring resonators) necessary for building large scale integrated circuits in suspended gallium arsenide (GaAs). Implementing PICs in suspended GaAs is a viable route towards achieving optimal system performance in areas with str…
Quantum information processing holds great promise for communicating and computing data efficiently. However, scaling current photonic implementation approaches to larger system size remains an outstanding challenge for realizing disruptive quantum technology. Two main ingredients of quantum information processors are quantum interference and single-photon detectors. Here we develop a hybrid superconducting-photonic circuit system to show how these elements can be combined in a scalable fashion on a silicon chip. We demonstrate the suitability of this approach for integrated quantum optics by …
Trapped ions are promising candidates for nodes of a scalable quantum network due to their long-lived qubit coherence times and high-fidelity single and two-qubit gates. Future quantum networks based on trapped ions will require a scalable way to route photons between different nodes. Photonic integrated circuits from fabrication foundries provide a compact solution to this problem. However, these circuits typically operate at telecommunication wavelengths which are incompatible with the strong dipole emissions of trapped ions. In this work, we demonstrate the routing of single photons from a …
The future of quantum photonic technology depends on the realization of efficient sources of single photons, the ideal carriers of quantum information. Parametric downconversion (PDC) is a promising route to create highly coherent, spectrally pure single photons for quantum photonics using versatile group-velocity matching (GVM) and tailored nonlinearities. However, the functionality to actively control the poling period of nonlinear crystals used in PDC is currently missing, yet would enable to dynamically modify the wavelength of single photons produced in the PDC process. Here a detailed GV…
