Toward large-scale fault-tolerant universal photonic quantum computing

Abstract

Photonic quantum computing is one of the leading approaches to universal quantum computation. However, large-scale implementation of photonic quantum computing has been hindered by its intrinsic difficulties, such as probabilistic entangling gates for photonic qubits and lack of scalable ways to build photonic circuits. Here we discuss how to overcome these limitations by taking advantage of two key ideas which have recently emerged. One is a hybrid qubit-continuous variable approach for realizing a deterministic universal gate set for photonic qubits. The other is time-domain multiplexing technique to perform arbitrarily large-scale quantum computing without changing the configuration of photonic circuits. These ideas together will enable scalable implementation of universal photonic quantum computers in which hardware-efficient error correcting codes can be incorporated. Furthermore, all-optical implementation of such systems can increase the operational bandwidth beyond THz in principle, utimately enabling large-scale fault-tolerant universal quantum computers with ultra-high operation frequency. arXiv:1904.07390v1 [quant-ph]

Continuous-wave 6-dB-squeezed light with 2.5-THz-bandwidth from single-mode PPLN waveguide

“…Quantum information processing (QIP) with quadrature amplitudes of light is promising for realizing deterministic, universal, and fault-tolerant operation. 1,2 In particular, continuouswave (CW) light enables efficient implementation of large-scale QIP with time-domain multiplexing (TDM) by using delay line interferometers. 3 This is because CW light provides full utilization of processing time, unlike pulsed light, which wastes most of the time due to its low duty ratio.…”

“…Applying TDM for QIP enables us, in principle, to generate unlimited scales of quantum entanglement in finite space. 1,4 Recently, large-scale quantum entanglement of over one-million states 5 and two-dimensional (2D) cluster states 6 have been successfully demonstrated by using TDM.…”

Learning the dynamics of open quantum systems from their steady states

“…The development of quantum simulators and computation devices has rapidly progressed over the last few years [1]. These developments span a multitude of physical platforms, including ultracold atoms [2][3][4][5], trapped ions [6][7][8], photonic circuits [9][10][11][12], Josephson junction arrays [13][14][15][16][17] and more, reaching ever larger complexity. The growth in the complexity of these systems calls for efficient methods to characterize and verify their dynamics.…”

Photon-Photon Quantum Phase Gate in a Photonic Molecule with χ(2) Nonlinearity

“…In this work, we propose an artificial atom on PIC by utilizing χ (2) nonlinearity in a well-engineered microresonator. The artificial atom has a size of microns, and is thus easy for fabrication and is scalable.…”

“…Artificial atom.- Figure 1(a) schematically illustrates the artificial atom, which is based on phase-matched χ (2) ultrahigh-Q microresonator. In the view of nonlinearly coupled optical modes, the system Hamiltonian reads [24,27] (h = 1)…”