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 the 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 terahertz in principle, ultimately enabling large-scale fault-tolerant universal quantum computers with ultrahigh operation frequency.

Highlights

  • With the promise of performing previously impossible computing tasks, quantum computing has received a lot of public attention

  • Photonic quantum computers have had intrinsic disadvantages which make scalable implementation almost impractical even though it is in principle scalable as shown by KLM

  • The two key ideas explained in this perspective—hybrid qubit-continuous variables (CVs) approach and time-domain multiplexing—are opening a new era in the history of photonic quantum computing, showing that scalable photonic quantum computing is possible

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Summary

INTRODUCTION

With the promise of performing previously impossible computing tasks, quantum computing has received a lot of public attention. The large bandwidth of photons provides high-speed (high clock frequency) operation in photonic quantum computers These advantageous features, together with mature technologies to prepare and manipulate photonic quantum states with linear optical elements and nonlinear crystals, have made photonic systems one of the leading approaches to building quantum computers.. It has recently been discovered that the time-domain multiplexing is even more powerful when combined with specific quantum computing schemes; time-domain multiplexed one-way quantum computation and a loop-based architecture for photonic quantum computing.20,21 These two schemes enable us to programmably perform arbitrarily large-scale quantum computing without changing the configuration of optical circuits. The schemes presented in this perspective are based only on linear optical components, and nonlinearity is fed from external sources as ancillary optical pulses only when required.22–24 This feature is advantageous to scale up quantum computers without introducing any additional sources of errors.

HYBRID QUANTUM COMPUTING
Qubit approach
CV approach
Hybrid qubit-CV approach
STRATEGY FOR LARGE-SCALE QUANTUM COMPUTING
Typical architecture for photonic quantum computing
Time-domain multiplexed one-way quantum computation
Loop-based architecture for photonic quantum computing
Technical challenges
CONCLUSION

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