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We demonstrate a large-scale tunable-coupling ring resonator array, suitable for high-dimensional classical and quantum transforms, in a CMOS-compatible silicon photonics platform. The device consists of a waveguide coupled to 15 ring-based dispersive elements with programmable linewidths and resonance frequencies. The ability to control both quality factor and frequency of each ring provides an unprecedented 30 degrees of freedom in dispersion control on a single spatial channel. This programmable dispersion control system has a range of applications, including mode-locked lasers, quantum key distribution, and photon-pair generation. We also propose a novel application enabled by this circuit – high-speed quantum communications using temporal-mode-based quantum data locking – and discuss the utility of the system for performing the high-dimensional unitary optical transformations necessary for a quantum data locking demonstration.

We present a network switch in the silicon-on-insulator platform capable of redistributing light to arbitrary outputs with continuously reconfigurable splitting ratios. We demonstrate software defined switching and physical-layer multicast of gigabit Ethernet.

A large-scale tunable-coupling ring resonator array is demonstrated in a CMOS-compatible silicon photonics platform to achieve tunable frequency-dependent group delay. The system is proposed for a phase-encoded quantum data locking protocol.

We present our progress in creating compact and scalable packaging to couple a 32 element fiber array to a corresponding array of single photon detectors for test at cryogenic temperatures. The packaging was thermally cycled down to 4.2 K to demonstrate stability.

Quantum information science offers inherently more powerful methods for communication, computation, and precision measurement that take advantage of quantum superposition and entanglement. In recent years, theoretical and experimental advances in quantum computing and simulation with photons have spurred great interest in developing large photonic entangled states that challenge today’s classical computers. As experiments have increased in complexity, there has been an increasing need to transition bulk optics experiments to integrated photonics platforms to control more spatial modes with higher fidelity and phase stability. The silicon-on-insulator (SOI) nanophotonics platform offers new possibilities for quantum optics, including the integration of bright, nonclassical light sources, based on the large third-order nonlinearity (χ(3)) of silicon, alongside quantum state manipulation circuits with thousands of optical elements, all on a single phase-stable chip. How large do these photonic systems need to be? Recent theoretical work on Boson Sampling suggests that even the problem of sampling from e30 identical photons, having passed through an interferometer of hundreds of modes, becomes challenging for classical computers. While experiments of this size are still challenging, the SOI platform has the required component density to enable low-loss and programmable interferometers for manipulating hundreds of spatial modes. Here, we discuss the SOI nanophotonics platform for quantum photonic circuits with hundreds-to-thousands of optical elements and the associated challenges. We compare SOI to competing technologies in terms of requirements for quantum optical systems. We review recent results on large-scale quantum state evolution circuits and strategies for realizing high-fidelity heralded gates with imperfect, practical systems. Next, we review recent results on silicon photonics-based photon-pair sources and device architectures, and we discuss a path towards large-scale source integration. Finally, we review monolithic integration strategies for single-photon detectors and their essential role in on-chip feed forward operations., United States. Air Force Office of Scientific Research (FA9550-14-1-0052), United States. Air Force Research Laboratory. RITA Program (FA8750-14-2-0120), American Society for Engineering Education. National Defense Science and Engineering Graduate Fellowship, National Science Foundation (U.S.). Graduate Research Fellowship Program (Grant 1122374).

We propose and analyze the design of a programmable photonic integrated circuit for high-fidelity quantum computation and simulation. We demonstrate that the reconfigurability of our design allows us to overcome two major impediments to quantum optics on a chip: it removes the need for a full fabrication cycle for each experiment and allows for compensation of fabrication errors using numerical optimization techniques. Under a pessimistic fabrication model for the silicon-on-insulator process, we demonstrate a dramatic fidelity improvement for the linear optics controlled-not and controlled-phase gates and, showing the scalability of this approach, the iterative phase estimation algorithm built from individually optimized gates. We also propose and simulate an experiment that the programmability of our system would enable: a statistically robust study of the evolution of entangled photons in disordered quantum walks. Overall, our results suggest that existing fabrication processes are sufficient to build a quantum photonic processor capable of high-fidelity operation.

Quantum random walks (QRWs) implemented in photonic media have seen significant recent attention for their applicability to problems in quantum simulation and quantum transport. However, performing statistically robust and high-fidelity studies of these problems has required either manual tuning of optical elements or the fabrication of multiple integrated photonic chips. Here, we present our recent theoretical and preliminary experimental results on the role of disorder and decoherence in QRWs implemented in a large-scale, programmable nanophotonic processor (PNP).

We present an architecture for programmable nanophotonic processors capable of arbitrary discrete transformations for quantum and classical applications. A method to combat fabrication imperfections with high fidelity is discussed along with initial experimental results.

Environmental noise and disorder play critical roles in quantum particle and wave transport in complex media, including solid-state and biological systems. Recent work has predicted that coupling between noisy environments and disordered systems, in which coherent transport has been arrested due to localization effects, could actually enhance transport. Photonic integrated circuits are promising platforms for studying such effects, with a central goal being the development of large systems providing low-loss, high-fidelity control over all parameters of the transport problem. Here, we fully map the role of disorder in quantum transport using a nanophotonic processor consisting of a mesh of 88 generalized beamsplitters programmable on microsecond timescales. Over 64,400 transport experiments, we observe several distinct transport regimes, including environment-assisted quantum transport and the ''quantum Goldilocks'' regime in strong, statically disordered discrete-time systems. Low loss and high-fidelity programmable transformations make this nanophotonic processor a promising platform for many-boson quantum simulation experiments., Comment: 4 figures, 8 pages

Quantum key distribution (QKD) enables participants to exchange secret information over long distances with unconditional security. However, the performance of today's QKD systems is subject to hardware limitations, such as those of available nonclassical-light sources and single-photon detectors. By encoding photons in high-dimensional states, the rate of generating secure information under these technical constraints can be maximized. Here, we demonstrate a complete time-energy entanglement-based QKD system with proven security against the broad class of arbitrary collective attacks. The security of the system is based on nonlocal dispersion cancellation between two time-energy entangled photons. This resource-efficient QKD system is implemented at telecommunications wavelength, is suitable for optical fiber and free-space links, and is compatible with wavelength-division multiplexing.

We design a resistive heater optimized for efficient and low-loss optical phase modulation in a silicon-on-insulator (SOI) waveguide and characterize the fabricated devices. Modulation is achieved by flowing current perpendicular to a new ridge waveguide geometry. The resistance profile is engineered using different dopant concentrations to obtain localized heat generation and maximize the overlap between the optical mode and the high temperature regions, while simultaneously minimizing optical loss due to free-carrier absorption. A 61.6 micrometer-long phase shifter was fabricated in a CMOS process with oxide cladding and two metal layers. The device features a phase-shifting efficiency of 24.77 +/- 0.43 mW/pi and a -3 dB modulation bandwidth of 130.0 +/- 5.59 kHz. The insertion loss measured for 21 devices across an 8-inch wafer was only 0.23 +/- 0.13 dB. Considering the prospect of densely integrated photonic circuits, we also quantify the separation necessary to isolate thermo-optic devices in the standard 220 nm SOI platform., This paper was published in Optics Express and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://dx.doi.org/10.1364/OE.22.010487. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law

Photonic-integrated circuits have emerged as a scalable platform for complex quantum systems. A central goal is to integrate single-photon detectors to reduce optical losses, latency and wiring complexity associated with off-chip detectors. Superconducting nanowire single-photon detectors (SNSPDs) are particularly attractive because of high detection efficiency, sub-50-ps jitter and nanosecond-scale reset time. However, while single detectors have been incorporated into individual waveguides, the system detection efficiency of multiple SNSPDs in one photonic circuit—required for scalable quantum photonic circuits—has been limited to, United States. Army Research Office (Defense Advanced Research Projects Agency. Information in a Photon (InPho) Program Grant W911NF-10-1-0416), National Science Foundation (U.S.) (Grant ECCS-1128222), United States. Air Force Office of Scientific Research. Multidisciplinary University Research Initiative (Grant FA9550-14-1-0052), Claude E. Shannon Fellowship, iQuISE Fellowship, National Science Foundation (U.S.). Integrative Graduate Education and Research Traineeship (Grant DGE-1069420), International Business Machines Corporation (Faculty Award)

A central aim of quantum information processing is the efficient entanglement of multiple stationary quantum memories via photons. Among solid-state systems, the nitrogen-vacancy centre in diamond has emerged as an excellent optically addressable memory with second-scale electron spin coherence times. Recently, quantum entanglement and teleportation have been shown between two nitrogen-vacancy memories, but scaling to larger networks requires more efficient spin-photon interfaces such as optical resonators. Here we report such nitrogen-vacancy-nanocavity systems in the strong Purcell regime with optical quality factors approaching 10,000 and electron spin coherence times exceeding 200 μs using a silicon hard-mask fabrication process. This spin-photon interface is integrated with on-chip microwave striplines for coherent spin control, providing an efficient quantum memory for quantum networks.

We implement a high-dimensional quantum key distribution protocol secure against collective attacks. We transform between conjugate measurement bases using group velocity dispersion. We obtain > 3 secure bits per photon coincidence.

We demonstrate an over-80-fold enhancement of an NV’s zero-phonon line emission inside cavity in the Purcell regime within a high-purity, electronic-grade diamond substrate. This system is a promising building block for quantum networks.

Single-photon high-dimensional quantum communication boosts photon efficiency and throughput. We report two time-energy-entanglement based quantum key distribution experiments --- one using dispersive optics, the other Franson interferometry --- with proven security against collective attacks.

We demonstrate the deterministic creation of nitrogen-vacancy spin qubits at the mode maximum of diamond photonic crystal cavities, enhancement of the zero-phonon-line spontaneous emission rate greater than 60, and NV spin phase coherence times exceeding 200µs.

CLEO: QELS--Fundamental Science, San Jose, California United States, June 9-14, 2013, We integrated superconducting nanowire single-photon detectors on sub-400-nm-thick silicon nitride membranes, which can then be transferred and aligned to photonic structures on a secondary chip with sub-micron placement accuracy.

High-dimensional quantum key distribution (HDQKD) offers the possibility of high secure-key rate with high photon-information efficiency. We consider HDQKD based on the time-energy entanglement produced by spontaneous parametric downconversion, and show that it is secure against collective attacks. Its security rests upon visibility data -- obtained from Franson and conjugate-Franson interferometers -- that probe photon-pair frequency correlations and arrival-time correlations. From these measurements an upper bound can be established on the eavesdropper's Holevo information by translating the Gaussian-state security analysis for continuous-variable quantum key distribution so that it applies to our protocol. We show that visibility data from just the Franson interferometer provides a weaker, but nonetheless useful, secure-key rate lower bound. To handle multiple-pair emissions, we incorporate the decoy-state approach into our protocol. Our results show that over 200\,km transmission distance in optical fiber, time-energy entanglement HDQKD could permit a 700 bit/sec secure-key rate, and a photon information efficiency of 2 secure-key bits per photon coincidence in the key-generation phase using receivers with 15% system efficiency., Comment: 17 pages, 2 figures

We directly assemble membrane-integrated superconducting-nanowire single- photon detectors (SNSPDs) on optical fiber-ferrule facets, yielding extremely compact, fiber-coupled SNSPD systems. Our initial demonstration shows 1% system detection efficien- cy, which can be further improved significantly.

We propose a high-dimensional quantum key distribution (QKD) protocol that employs temporal correlations of entangled photons. The security of the protocol relies on measurements by Alice and Bob in one of two conjugate bases, implemented using dispersive optics. We show that this dispersion-based approach is secure against general coherent attacks. The protocol is additionally compatible with standard fiber telecommunications channels and wavelength division multiplexers. We offer multiple implementations to enhance the transmission rate and describe a heralded qudit source that is easy to implement and enables secret-key generation at up to 100 Mbps at over 2 bits per photon., 5 pages, 3 figures. v2 contains details of security analysis previously left to Supplemental Information (not included in v1)

We propose a high-dimensional quantum key distribution (QKD) protocol suitable for integration with telecommunication infrastructure. The key is generated by the temporal correlations of photons measured in mutually unbiased bases using dispersive optics.

We present a protocol for generating on-demand, indistinguishable single photons on a silicon photonic integrated chip. The source is a time-multiplexed spontaneous parametric down-conversion element that allows optimization of single-photon versus multiphoton emission while realizing high output rate and indistinguishability. We minimize both the scaling of active elements and the scaling of active element loss with multiplexing. We then discuss detection strategies and data processing to further optimize the procedure. We simulate an improvement in single-photon-generation efficiency over previous time-multiplexing protocols, assuming existing fabrication capabilities. We then apply this system to generate heralded Bell states. The generation efficiency of both nonclassical states could be increased substantially with improved fabrication procedures., 7 pages, 4 figures

We present a general approach for coupling a specific mode in a planar photonic crystal (PC) waveguide to a desired free-space mode. We apply this approach to a W1 PC waveguide by introducing small index perturbations to selectively couple a particular transverse mode to an approximately Gaussian, slowly diverging free space mode. This "perturbative photonic crystal waveguide coupler" (PPCWC) enables efficient interconversion between selectable propagating photonic crystal and free space modes with minimal design perturbations., 11 pages, 8 figures

We introduce a reconfigurable silicon quantum photonic network for implementing general linear optics transformations in the spatial mode basis. This network enables implementation of a range of quantum algorithms; we discuss the phase estimation algorithm.