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Conference on Lasers and Electro-Optics

Generation of Schrödinger’s cat state in an optical double sideband mode

Takahiro Serikawa, Jun–ichi Yoshikawa, Hidehiro Yonezawa, Timothy C. Ralph, Elanor H. Huntington, Akira Furusawa

Published Jan 1, 2018• 0 citations
Publisher

Abstract

An optical Schrodigner's cat state is generated in 500.6 MHz double sideband mode of continuous wave light. We used phase modulation to selectively subtract a photon from sideband. The reconstructed Wigner function exhibits a significant negativity of -0.088 ± 0.001 without any correction.
DOI
10.1364/cleo_qels.2018.fth4g.6

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We propose a method to subtract a photon from a double sideband mode of continuous-wave light. The central idea is to use phase modulation as a frequency sideband beam splitter in the heralding photon subtraction scheme, where a small portion of the sideband mode is down-converted to 0 Hz to provide a trigger photon. An optical cat state is created by applying the proposed method to a squeezed state at 500 MHz sideband, which is generated by an optical parametric oscillator. The Wigner function of the cat state reconstructed from a direct homodyne measurement of the 500 MHz sideband modes shows the negativity of W(0,0)=-0.088±0.001 without any loss corrections.
We have generated and measured an approximation of an optical Schrödinger cat state by photon subtraction from a squeezed state. Using single-photon avalanche photodiode detectors and photon-number-resolving transition edge sensors, we were able to extract Wigner distributions for one or two photons subtracted from the squeezed state, resulting in both an odd and even cat state. The one-photon-subtracted Wigner distribution shows measured negative features (without any correction), indicating quantum character. The Wigner distribution of the two-photon-subtracted state is negative after correcting for homodyne losses. A full statistical analysis is under way to quantify the magnitude and fidelity of the cat states generated.
Until now, Schrödinger's cat states are generated by subtracting single photons from the whole bandwidth of squeezed vacua. However, it was pointed out recently that the achievable purities are limited in such method (J. Yoshikawa, W. Asavanant, and A. Furusawa, arXiv:1707.08146 [quant-ph] (2017)). In this paper, we used our new photon subtraction method with a narrowband filtering cavity and generated a highly pure Schrödinger's cat state with the value of −0.184-0.184−0.184 at the origin of the Wigner function. To our knowledge, this is the highest value ever reported without any loss corrections. The temporal mode also becomes exponentially rising in our method, which allows us to make a real-time quadrature measurement on Schrödinger's cat states, and we obtained the value of −0.162-0.162−0.162 at the origin of the Wigner function.
We propose a high-rate generation method of optical Schrödinger cat states [1] . More than a decade, the standard method of cat-state generation has been photon subtraction from squeezed vacuum states [2] . Its constraints on experimental parameters, however, limit the generation rate. We overcome the problem by considering photon-number measurement in one mode of arbitrary two-mode Gaussian states, which we call "generalized photon subtraction". Analysis of such a general situation is challenging, but we analytically derive an efficient condition by describing the state-generation process using wave functions. Supposing realistic experimental conditions, the generation rate of cat states with large-amplitude (| α| ≥ 2) is improved by multiple orders from the conventional photon subtraction. Our proposal would open a way for quantum error correction and coherent-state-based quantum computing.
Non-Gaussian states are essential resources for universal, fault-tolerant optical quantum computing, but their generation rate remains limited by low heralding probabilities and operation in nanosecond temporal modes. Here, we demonstrate multi-photon generalized photon subtraction in picosecond optical wave packets, establishing the state-generation capability required for high-rate operation by addressing the temporal-mode bottleneck that has constrained the achievable rate. Two interfering ultrashort squeezed vacua are heralded by photon-number-resolving detection with a high-speed transition-edge sensor and characterized by pulsed homodyne detection matched to 10-ps temporal modes at a 5-MHz pump repetition rate. We reconstruct Wigner functions without loss correction that exhibit up to four distinct negative regions for four-photon heralding, together with an effective cat-state amplitude of αeff=1.69α_{\mathrm{eff}} = 1.69αeff​=1.69. This amplitude approaches the range of practical relevance for fault-tolerant cat-code architectures and for adaptive breeding toward logical-qubit generation, while the picosecond temporal mode establishes a platform compatible with high-rate, scalable time-multiplexed photonic architectures.