32 research outputs found
Quantum state correction using a measurement-based feedforward mechanism
One of the weaknesses of quantum optical state postselection schemes is the low success probability. Typically there is a trade-off between amplifier properties such as success probability and output state fidelity. However, here we present a state comparison amplifier for optical coherent states, which features an active measurement and feedforward mechanism to correct for errors made during the initial amplification. The simple and relatively low latency mechanism allows us to correct for a binary phase alphabet. We demonstrate a significant simultaneous improvement in the amplifier characteristic parameters: output state fidelity, correct state fraction, and success probability. This demonstrates that nondeterministic quantum amplification can be enhanced significantly by measurement and feedforward
Time-bin encoding for optical quantum computing
Scalability has been a longstanding issue in implementing large-scale photonic experiments for optical quantum computing. Traditional encodings based on the polarisation or spatial degrees of freedom become extremely resource-demanding when the number of modes becomes large, as the need for many nonclassical sources of light and the number of beam splitters required become unfeasible. Alternatively, time-bin encoding paves the way to overcome some of these limitations, as it only requires a single quantum light source and can be scaled to many temporal modes through judicious choice of pulse sequence and delays. Such an apparatus constitutes an important step toward large-scale experiments with low resource consumption.
This work focuses on the time-bin encoding implementation. First, we assess its feasibility by thoroughly investigating its performance through numerical simulations under realistic conditions. We identify the critical components of the architecture and find that it can achieve performances comparable to state-of-the-art devices. Moreover, we consider two implementation approaches, in fibre and free space, and enumerate their strengths and weaknesses. Subsequently, we delve into the lab to explore these schemes and the key components involved therein. For the fibre case, we report the first implementation of time-bin encoded Gaussian boson sampling and use the samples obtained from the device to search for dense subgraphs of sizes three and four in a 10-node graph.
Finally, we complement the study of the time-bin encoding with two side projects that contribute to the broad spectrum of enabling techniques for quantum information science. First, we demonstrate the ability to perform photon-number resolving measurements with a commercial superconducting nanowire single-photon detector system and apply it to improve the statistics of a heralded single-photon source. Second, we demonstrate that by employing a phase-tunable coherent state, we can fully characterise a multimode Gaussian state through solely the low-order photon statistics.Open Acces
Hybrid integration methods for on-chip quantum photonics
The goal of integrated quantum photonics is to combine components for the generation, manipulation, and detection of nonclassical light in a phase-stable and efficient platform. Solid-state quantum emitters have recently reached outstanding performance as single-photon sources. In parallel, photonic integrated circuits have been advanced to the point that thousands of components can be controlled on a chip with high efficiency and phase stability. Consequently, researchers are now beginning to combine these leading quantum emitters and photonic integrated circuit platforms to realize the best properties of each technology. In this paper, we review recent advances in integrated quantum photonics based on such hybrid systems. Although hybrid integration solves many limitations of individual platforms, it also introduces new challenges that arise from interfacing different materials. We review various issues in solid-state quantum emitters and photonic integrated circuits, the hybrid integration techniques that bridge these two systems, and methods for chip-based manipulation of photons and emitters. Finally, we discuss the remaining challenges and future prospects of on-chip quantum photonics with integrated quantum emitters. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen
Encoding qubits into oscillators with atomic ensembles and squeezed light
The Gottesman-Kitaev-Preskill (GKP) encoding of a qubit within an oscillator
provides a number of advantages when used in a fault-tolerant architecture for
quantum computing, most notably that Gaussian operations suffice to implement
all single- and two-qubit Clifford gates. The main drawback of the encoding is
that the logical states themselves are challenging to produce. Here we present
a method for generating optical GKP-encoded qubits by coupling an atomic
ensemble to a squeezed state of light. Particular outcomes of a subsequent spin
measurement of the ensemble herald successful generation of the resource state
in the optical mode. We analyze the method in terms of the resources required
(total spin and amount of squeezing) and the probability of success. We propose
a physical implementation using a Faraday-based quantum non-demolition
interaction.Comment: (v2) consistent with published version; (v1) 16 pages, 5 figure
Quantum interferometers: principles and applications
Interference, which refers to the phenomenon associated with the
superposition of waves, has played a crucial role in the advancement of physics
and finds a wide range of applications in physical and engineering
measurements. Interferometers are experimental setups designed to observe and
manipulate interference. With the development of technology, many quantum
interferometers have been discovered and have become cornerstone tools in the
field of quantum physics. Quantum interferometers not only explore the nature
of the quantum world but also have extensive applications in quantum
information technology, such as quantum communication, quantum computing, and
quantum measurement. In this review, we analyze and summarize three typical
quantum interferometers: the Hong-Ou-Mandel (HOM) interferometer, the N00N
state interferometer, and the Franson interferometer. We focus on the
principles and applications of these three interferometers. In the principles
section, we present the theoretical models for these interferometers, including
single-mode theory and multi-mode theory. In the applications section, we
review the applications of these interferometers in quantum communication,
computation, and measurement. We hope that this review article will promote the
development of quantum interference in both fundamental science and practical
engineering applications.Comment: 64 pages, 40 figures. Comments are welcom