Most of the architectural research on photonic implementations of measurement-based quantum computing (MBQC) has focused on the quantum resources involved in the problem with the implicit assumption that these will provide the main constraints on system scaling. However, the `flying-qubit' architecture of photonic MBQC requires specific timing constraints that need to be met by the classical control system. This classical control includes, for example: the amplification of the signals from single-photon detectors to voltage levels compatible with digital systems; the implementation of a control system which converts measurement outcomes into basis settings for measuring subsequent cluster qubits, in accordance with the quantum algorithm being implemented; and the digital-to-analog converter (DAC) and amplifier systems required to set these measurement bases using a fast phase modulator. In this paper, we analyze the digital system needed to implement arbitrary one-qubit rotations and controlled-NOT (CNOT) gates in discrete-variable photonic MBQC, in the presence of an ideal cluster state generator, with the main aim of understanding the timing constraints imposed by the digital logic on the analog system and quantum hardware. We use static timing analysis of a Xilinx FPGA (7 series) to provide a practical upper bound on the speed at which the adaptive measurement processing can be performed, in turn constraining the photonic clock rate of the system. Our work points to the importance of co-designing the classical control system in tandem with the quantum system in order to meet the challenging specifications of a photonic quantum computer.
Travelling-wave single-photon detectors integrated with diamond photonic circuits - operation at visible and telecom wavelengths with a timing jitter down to 23 ps
Integrated quantum photonics, which allows for the development and implementation of chip-scale devices, is recognized as a key enabling technology on the road towards scalable quantum networking schemes. However, many state-of-the-art integrated quantum photonics demonstrations still require the coupling of light to external photodetectors. On-chip silicon single-photon avalanche diodes (SPADs) provide a viable solution as they can be seamlessly integrated with photonic components, and operated with high efficiencies and low dark counts at temperatures achievable with thermoelectric cooling. …
In the context of ultra-fast quantum communication and random number generation, detection timing-jitters represent a strong limitation as they can introduce major time-tagging errors and affect the quality of time-correlated photon counting or quantum state engineering. Despite their importance in emerging photonic quantum technologies, no detector model including such effects has been developed so far. We propose here an operational theoretical model based on POVM density formalism able to explicitly quantify the effect of timing-jitter for a typical class of single photon detector. We apply…
We report upon a novel principle for realization of a fast nondeterministic random number generator whose randomness relies on intrinsic randomness of the quantum physical processes of photonic emission in semiconductors and subsequent detection by the photoelectric effect. Timing information of detected photons is used to generate binary random digits-bits. The bit extraction method based on restartable clock theoretically eliminates both bias and autocorrelation while reaching efficiency of almost 0.5 bits per random event. A prototype has been built and statistically tested.
Quantum algorithms need to be compiled to respect the constraints imposed by quantum processors, which is known as the mapping problem. The mapping procedure will result in an increase of the number of gates and of the circuit latency, decreasing the algorithm's success rate. It is crucial to minimize mapping overhead, especially for Noisy Intermediate-Scale Quantum (NISQ) processors that have relatively short qubit coherence times and high gate error rates. Most of prior mapping algorithms have only considered constraints such as the primitive gate set and qubit connectivity, but the actual g…
With the rapid development of microwave photonics, which has expanded to numerous applications of commercial importance, eliminating the emerging bottlenecks becomes of vital importance. For example, as the main branch of microwave photonics, radio-over-fiber technology provides high bandwidth, low-loss, and long-distance propagation capability, facilitating wide applications ranging from telecommunication to wireless networks. With ultrashort pulses as the optical carrier, huge capacity is further endowed. However, the wide bandwidth of ultrashort pulses results in the severe vulnerability of…
Optimizing a connection through a quantum repeater network requires careful attention to the photon propagation direction of the individual links, the arrangement of those links into a path, the error management mechanism chosen, and the application's pattern of consuming the Bell pairs generated. We analyze combinations of these parameters, concentrating on one-way error correction schemes (1-EPP) and high success probability links (those averaging enough entanglement successes per round trip time interval to satisfy the error correction system). We divide the buffering time (defined as minim…
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…
Non-destructive detection of photonic qubits will enable important applications in photonic quantum information processing and quantum communications. Here, we present an approach based on a solid-state cavity containing an ensemble of rare-earth ions. First a probe pulse containing many photons is stored in the ensemble. Then a single signal photon, which represents a time-bin qubit, imprints a phase on the ensemble that is due to the AC Stark effect. This phase does not depend on the exact timing of the signal photon, which makes the detection insensitive to the time-bin qubit state. Then th…
Multi-photon interference is at the heart of photonic quantum technologies. Arrays of integrated cavities can support bright sources of single-photons with high purity and small footprint, but the inevitable spectral distinguishability between photons generated from non-identical cavities is an obstacle to scaling. In principle, this problem can be alleviated by measuring photons with high timing resolution, which erases spectral information through the time-energy uncertainty relation. Here, we experimentally demonstrate that detection can be implemented with a temporal resolution sufficient …
Designing Nonlinear Photonic Crystals for High-Dimensional Quantum State Engineering
Technion（以色列理工学院）；Tel Aviv University（特拉维夫大学）；Massachusetts Institute of Technology（麻省理工学院）；Physical Research Laboratory（物理研究实验室）；Verily Research（Verily研究院）
Two-electron charged self-assembled quantum dot molecules exhibit a decoherence-avoiding singlet-triplet qubit subspace and an efficient spin-photon interface. We demonstrate quantum entanglement between emitted photons and the spin-qubit after the emission event. We measure the overlap with a fully entangled state to be $69.5\pm2.7\,\%$, exceeding the threshold of $50\,\%$ required to prove the non-separability of the density matrix of the system. The photonic qubit is encoded in two photon states with an energy difference larger than the timing resolution of existing detectors. We devise a n…
The development of quantum computers and quantum simulators promises to provide solutions to problems, which can currently not be solved on classical computers. Finding the best physical implementation for such technologies is an important research topic and using optical effects is a promising route towards this goal. It was theoretically shown that optical quantum computing is possible using only single-photon sources and detectors, and linear optical circuits. An experimental implementation of such quantum optical circuits requires a stable, robust and scalable architecture. This can be ach…
In this article, we introduce a framework for entanglement characterization by time-resolved single-photon counting with measurement operators defined in the time domain. For a quantum system with unitary dynamics, we generate time-continuous measurements by shifting from the Schrodinger picture to the Heisenberg representation. In particular, we discuss this approach in reference to photonic tomography. To make the measurement scheme realistic, we impose timing uncertainty on photon counts along with the Poisson noise. Then, the framework is tested numerically on quantum tomography of qubits.…
