arXiv subjects

Yoshichika Miwa

Publications and source records attributed to Yoshichika Miwa.

7 recordsLinked to original sources

arXiv2014

Exploring a new regime for processing optical qubits: squeezing and unsqueezing single photons

We implement the squeezing operation as a genuine quantum gate, deterministically and reversibly acting `online' upon an input state no longer restricted to the set of Gaussian states. More specifically, by applying an efficient and robust squeezing operation for the first time to non-Gaussian states, we demonstrate a two-way conversion between a particle-like single-photon state and a wave-like superposition of coherent states. Our squeezing gate is reliable enough to preserve the negativities of the corresponding Wigner functions. This demonstration represents an important and necessary step towards hybridizing discrete and continuous quantum protocols.

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arXiv2011

Parallel generation of quadripartite cluster entanglement in the optical frequency comb

Scalability and coherence are two essential requirements for the experimental implementation of quantum information and quantum computing. Here, we report a breakthrough toward scalability: the simultaneous generation of a record 15 quadripartite entangled cluster states over 60 consecutive cavity modes (Qmodes), in the optical frequency comb of a single optical parametric oscillator. The amount of observed entanglement was constant over the 60 Qmodes, thereby proving the intrnisic scalability of this system. The number of observable Qmodes was restricted by technical limitations, and we conservatively estimate the actual number of similar clusters to be at least three times larger. This result paves the way to the realization of large entangled states for scalable quantum information and quantum computing.

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arXiv2011

Reversing Quantum Nondemolition Interaction as Quantum Erasing

We reverse a quantum nondemolition (QND) interaction and restore the signal quantum state by measurement and feedforward. This operation corresponds to quantum erasing for continuous variables (CVs). CV quantum eraser restores the coherence of the signal quantum state by erasing the signal information leaking to another system, where the information leaking is induced by the QND interaction. We employ a homodyne measurement for erasing of the information. Then, by performing a feedforward displacement operation, we restore the initial quantum state together with its coherence. For verification, we use a coherent state and a squeezed vacuum state as inputs, and then restore one of them or the other, whichever we choose. Experimental results are shown as Wigner functions, average fidelity, change in coherence, and trade-off between leakage information and coherence.

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arXiv2011

Demonstration of reversible phase-insensitive optical amplifier

We experimentally demonstrate phase-insensitive linear optical amplification which preserves the idler at the output. Since our amplification operation is unitary up to small excess noise, it is reversible beyond the classical limit. The entanglement between the two output modes is the resource for the reversibility. The amplification gain of 2.0 is demonstrated. In addition, combining this amplifier with a beamsplitter, we also demonstrate approximate cloning of coherent states where an anticlone is present. We investigate the reversibility by reconstructing the initial state from the output correlations, and the results are slightly beyond the cloning limit. Furthermore, full characterization of the amplifier and cloner is given by using coherent states with several different mean values as inputs. Our amplifier is based on linear optics, offline preparation of nonclassical ancillas, and homodyne measurements followed by feedforward. Squeezed states are used as the ancillas, and nonlinear optical effects are exploited only for their generation. The ancillas introduce nonclassicality into the amplifying operation, making entanglement at the output.

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arXiv2010

Demonstration of Cluster State Shaping and Quantum Erasure for Continuous Variables

We demonstrate experimentally how to remove an arbitrary node from a continuous-variable cluster state and how to shorten any quantum wires of such a state. These two basic operations, performed in an unconditional fashion, are a manifestation of quantum erasure and can be employed to obtain various graph states from an initial cluster state. Starting with a sufficiently large cluster, the resulting graph states can then be used for universal quantum information processing. In the experiment, all variations of this cluster-shaping are demonstrated on a four-mode linear cluster state through homodyne measurements and feedforward.

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arXiv2009

Demonstration of a universal one-way quantum quadratic phase gate

We demonstrate a quadratic phase gate for one-way quantum computation in the continuous-variable regime. This canonical gate, together with phase-space displacements and Fourier rotations, completes the set of universal gates for realizing any single-mode Gaussian transformation such as arbitrary squeezing. As opposed to previous implementations of measurement-based squeezers, the current gate is fully controlled by the local oscillator phase of the homodyne detector. Verifying this controllability, we give an experimental demonstration of the principles of one-way quantum computation over continuous variables. Moreover, we can observe sub-shot-noise quadrature variances in the output states, confirming that nonclassical states are created through cluster computation.

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arXiv2008

Demonstration of a quantum nondemolition sum gate

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 fields. We experimentally demonstrate a QND sum gate, employing the scheme by R. Filip, P. Marek, and U.L. Andersen [\pra {\bf 71}, 042308 (2005)], solely based on offline 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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