Creation, Storage, and On-Demand Release of Optical Quantum States with a Negative Wigner Function

Jun-Ichi Yoshikawa,Shintaro Kurata,Peter Van Loock,Kenzo Makino,Akira Furusawa

doi:10.1103/physrevx.3.041028

Jun-Ichi Yoshikawa, Shintaro Kurata + Show 3 more

Open Access

https://doi.org/10.1103/physrevx.3.041028

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Abstract

Highly nonclassical quantum states of light, characterized by Wigner functions with negative values, have been created so far only in a heralded fashion. In this case, the desired output emerges rarely and randomly from a quantum-state generator. An important example is the heralded production of high-purity single-photon states, typically based on some nonlinear optical interaction. In contrast, on-demand single-photon sources were also reported, exploiting the quantized level structure of matter systems. These sources, however, lead to highly impure output states, composed mostly of vacuum. While such impure states may still exhibit certain single-photon-like features such as anti-bunching, they are not enough nonclassical for advanced quantum information processing. On the other hand, the intrinsic randomness of pure, heralded states can be circumvented by first storing and then releasing them on demand. Here we propose such a controlled release, and we experimentally demonstrate it for heralded single photons. We employ two optical cavities, where the photons are both created and stored inside one cavity, and finally released through a dynamical tuning of the other cavity. We demonstrate storage times of up to 300 ns, while keeping the single-photon purity around 50% after storage. This is the first demonstration of a negative Wigner function at the output of an on-demand photon source or a quantum memory. In principle, our storage system is compatible with all kinds of nonclassical states, including those known to be essential for many advanced quantum information protocols.

Highlights

Representing flying quantum information, photons are ideally suited for communication between the stations of a quantum network [1,2]
The output quantum states are characterized by optical homodyne detection
Homodyne detection employs interference with a strong local-oscillator light beam, and it indicates the photons’ coherence and their tunability to some specific wavelength

Summary

INTRODUCTION

Representing flying quantum information, photons are ideally suited for communication between the stations of a quantum network [1,2]. In contrast to the highly restrictive wavelengths of existing on-demand sources, basically determined by the corresponding energy levels of matter, the heralded approach allows for a broader range of wavelengths, in particular, including the telecom wavelength [24] Owing to these advantages, the most advanced quantum-information experiments have been demonstrated with such heralded schemes [8,9,10,11,12]. We have succeeded for the first time in acquiring, effectively on demand (see above), a quantum feature as strong as the negativity of the Wigner function This feature is essentially different from the more conventional single-photon character of antibunching [18], which is immune to linearoptical losses and valid even for sources with very low purity. Our system may function as a universal quantum memory, where optical, flying quantum information of arbitrary dimension is written into the memory via unconditional continuous-variable quantum teleportation [11,12] and later recalled on demand

WORKING PRINCIPLE

EXPERIMENTAL RESULTS AND METHODS

Procedure

Cavity configuration

Verification

CONCLUSION AND DISCUSSION