Efficient backcasting search for optical quantum state synthesis

Abstract

Non-Gaussian states are essential for many quantum technologies with continuous variables. The so-called optical quantum state synthesizer (OQSS), consisting of Gaussian input states, linear optics, and photon-number resolving detectors, is a promising method for non-Gaussian state preparation. However, an inevitable and crucial problem is the complexity of the numerical simulation of the state preparation on a classical computer.To remedy this, we offer an efficient scheme employing a backcasting approach, where the circuit of OQSS is devided into some sublayers, and we simulate the OQSS backwards from final to first layers. As an important example and application, we numerically show that the proposed OQSS allows us to simulate the generation of the Gottesman-Kitaev-Preskill qubit with a fidelity sufficient for universality and fault tolerance in optical quantum computation. Moreover, our results show that the detected photon number by each detector is at most 2, which can significantly reduce the requirements for the photon-number resolving detector. Further, by virtue of the potential for the preparation of a wide variety of non-Gaussian states, the proposed OQSS can be a key ingredient in general optical quantum information processing.

Switching-free time-domain optical quantum computation with quantum teleportation

“…Regarding the preparation of the GKP qubit which is required in most of the optical quantum computation architecture, although there are recent realizations in iontrapped system [43] and superconducting system [44] and the optical generation has not been achieved yet, there are a few promising theoretical proposals (see, for example Ref. [45][46][47]). Also, development of optical quantum memory capable of storing multiphoton quantum state such as GKP state is being developed [27,48].…”

Building a large-scale quantum computer with continuous-variable optical technologies

“…Thus, the qunaught state reduces the noise in the entangled pair, which is expected to improve the threshold of the squeezing level. In superconducting circuit and ion trap systems, the GKP qubit has been realized recently [184,185], and the efficient preparation of the GKP qubit has been extensively studied [57,217,[254][255][256][257][258]. In an optical setup, to the best of our knowledge, the GKP qubit has not been realized, although there are several approaches such as the breeding protocol [255,259], the use of photon-number resolving detectors [258,260], the use of the interaction between light and matter qubits [261][262][263], the use of the cross-Kerr interaction [264,265], and so on.…”

“…In fact, the complexity of the calculation of a hafnian has been used for achieving quantum supremacy over a classical computer by a protocol called GBS [7,269]. Recently, the efficient backcasting search has been developed to solve the problem of time complexity for arbitrary non-Gaussian state generation [258]. Also, Ref.…”

Analysis of optical quantum state preparation using photon detectors in the finite-temporal-resolution regime

“…However, most of previous experiments have generated only simple non-Gaussian states such as a Schrödinger's cat state or a fock state using on-off detectors, which discriminate only the presence or absence of photons [14][15][16][17][18]. In order to prepare practical non-Gaussian states for quantum computation such as GKP state [9], it is necessary to use a PNRD capable of multiphoton detection [19,20].…”