Kan Takase

We propose a high-rate generation method of optical Schr\"odinger cat states. Thus far, photon subtraction from squeezed vacuum states has been a standard method in cat-state generation, but its constraints on experimental parameters limit the generation rate. In this paper, we consider the state generation by photon number measurement in one mode of two-mode Gaussian states, which is a generalization of conventional photon subtraction, and derive the conditions to generate high-fidelity and lar

Continuous-wave (CW) squeezed light is used in the generation of various optical quantum states, and thus is a fundamental resource of fault-tolerant universal quantum computation using optical continuous variables. To realize a practical quantum computer, a waveguide optical parametric amplifier (OPA) is an attractive CW squeezed light source in terms of its THz-order bandwidth and suitability for modularization. The usages of a waveguide OPA in quantum applications thus far, however, are limit

Abstract Practical quantum computing requires robust encoding of logical qubits in physical systems to protect fragile quantum information. Currently, the lack of scalability limits the logical encoding in most physical systems, and thus the high scalability of propagating light can be a game changer. However, propagating light also has difficulty in logical encoding due to weak nonlinearity. Here, we propose a synthesizer that encodes Gottesman-Kitaev-Preskill (GKP) qubits in propagating light

The generation of a logical qubit called the Gottesman-Kitaev-Preskill (GKP) qubit in an optical traveling wave is a major challenge for realizing large-scale universal fault-tolerant optical quantum computers. Recently, probabilistic generation of elementary GKP qubits has been demonstrated using photon number measurements and homodyne measurements. However, the generation rate is only a few Hz, and it will be difficult to generate fault-tolerant GKP qubits at a practical rate unless success pr

Controlling the temporal waveform of light is the key to a versatile light source in classical and quantum electronics. Although pulse shaping of classical light is mature and has been used in various fields, more advanced applications would be realized by a light source that generates arbitrary quantum light with arbitrary temporal waveforms. We call such a device a quantum arbitrary waveform generator (Q-AWG). The Q-AWG must be able to handle various quantum states of light, which are fragile.

A method to reconstruct single and dual temporal modes of non-Gaussian states is devised and experimentally tested. The idea is based on principal component analysis and a dual homodyne measurement, allowing the measurement of complex temporal modes.

Practical quantum computing requires robust encoding of logical qubits in physical systems to protect fragile quantum information. Currently, the lack of scalability limits the logical encoding in most physical systems, and thus the high scalability of propagating light can be a game changer for realizing a practical quantum computer. However, propagating light also has a drawback: the difficulty of logical encoding due to weak nonlinearity. Here, we propose Gaussian breeding that encodes arbitr

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 challengi

Controlling the waveform of light is the key for a versatile light source in classical and quantum electronics. Although pulse shaping of classical light is a mature technique and has been used in various fields, more advanced applications would be realized by a light source that generates arbitrary quantum light with arbitrary temporal waveform. We call such a device a quantum arbitrary waveform generator (Q-AWG). The Q-AWG must be able to handle versatile quantum states of light, which are fra

We formulate a method to efficiently extract the non-classicality of photon number measurements into optical traveling wave and show that practical logical qubits can be generated over 10% probability in a realistic system.