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arXiv:1712.08411 · Physical Review A

Quantum nondemolition gate operations and measurements in real time on fluctuating signals

Yu Shiozawa, Jun–ichi Yoshikawa, Shota Yokoyama, Toshiyuki Kaji, Kenzo Makino, Takahiro Serikawa, Ryosuke Nakamura, Shigenari Suzuki, Shota Yamazaki, Warit Asavanant, Shuntaro Takeda, Peter van Loock, Akira Furusawa

Published Nov 9, 2018• 22 citations
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Abstract

We demonstrate an optical quantum nondemolition (QND) interaction gate with a bandwidth of about 100 MHz. Employing this gate, we are able to perform QND measurements in real time on randomly fluctuating signals. Our QND gate relies on linear optics and offline-prepared squeezed states. In contrast to previous demonstrations on narrow sideband modes, our gate is compatible with quantum states temporally localized in a wave-packet mode including non-Gaussian quantum states. This is the cornerstone of realizing quantum error correction and universal gate operations.

DOI
10.1103/physreva.98.052311

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We demonstrate an optical quantum nondemolition (QND) interaction gate with a bandwidth of about 100 MHz. Employing this gate, we are able to perform QND measurements in real time on randomly fluctuating signals. Our QND gate relies on linear optics and offline-prepared squeezed states. In contrast to previous demonstrations on narrow sideband modes, our gate is compatible with quantum states temporally localized in a wave-packet mode including non-Gaussian quantum states. This is the cornerstone of realizing quantum error correction and universal gate operations.
The sum gate is the canonical two-mode gate for universal quantum computation based on continuous quantum variables. It represents the natural analogue to a qubit C-NOT gate. In addition, the continuous-variable gate describes a quantum nondemolition (QND) interaction between the quadrature components of two light modes. We experimentally demonstrate a QND sum gate, employing the scheme by R. Filip, P. Marek, and U. L. Andersen [Phys. Rev. A 71, 042308 (2005)10.1103/PhysRevA.71.042308], solely based on off-line squeezed states, homodyne measurements, and feedforward. The results are verified by simultaneously satisfying the criteria for QND measurements in both conjugate quadratures.
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Non-Gaussian quantum gates are essential components for optical quantum information processing. However, the efficient implementation of practically important multimode higher-order non-Gaussian gates has not been comprehensively studied. We propose a measurement-based method to directly implement general, multimode, and higher-order non-Gaussian gates using only fixed non-Gaussian ancillary states and adaptive linear optics. Compared to existing methods, our method allows for a more resource-efficient and experimentally feasible implementation of multimode gates that are important for various applications in optical quantum technology, such as the two-mode cubic quantum nondemolition gate or the three-mode continuous-variable Toffoli gate, and their higher-order extensions. Our results will expedite the progress toward fault-tolerant universal quantum computing with light. Published by the American Physical Society 2024
Continuous quantum nondemolition (QND) measurements of the amplitude quadrature of a 1064 nm wave are performed with a monolithic dual-port degenerate optical parametric amplifier (OPA). The quality of the measurement is limited in part by the quantum fluctuations carried by the vacuum meter input wave. Improved QND measurements are realized by injecting 3.4 dB amplitude-squeezed light into the meter input port of the OPA. This achieves increased squeezing and correlation of the output signal and meter waves, and both improved operation as a quantum optical tap and as a quantum state preparator. The all-solid-state system was operated for 5 h with high stability.
Summary form only given. The present techniques allow one to perform continuous or discrete quantum measurements at or even beyond the standard "quantum noise" level, even on single quantum objects. In this context, Kip Thorne and Vladimir Braginsky introduced in the seventies the concept of "Quantum Non Demolition (QND) measurement", which was initially meant to be applied to mechanical harmonic oscillators designed for detecting gravitational waves, the so-called "Weber's bars". But the QND ideas encountered a real success in quantum optics, where quantum fluctuations are readily accessible, and can also be circumvented. We review the state of the art of QND measurements, in this broad sense of sub-shot-noise optical information processing. Most of the initial objectives of QND measurements have now been successfully reached through proof-of-principle experiments. The domain is now opening on future perspectives related to quantum information processing (e.g. quantum cryptography), either with "discrete" or "continuous" quantum variables. In this context the close relationship between QND measurements and controlled-NOT (CNOT) gates are discussed and illustrated.