Universal Quantum Computing with Measurement-Induced Continuous-Variable Gate Sequence in a Loop-Based Architecture

We propose a scalable scheme for optical quantum computing using measurement-induced continuous-variable quantum gates in a loop-based architecture. Here, time-bin-encoded quantum information in a single spatial mode is deterministically processed in a nested loop by an electrically programmable gate sequence. This architecture can process any input state and an arbitrary number of modes with almost minimum resources, and offers a universal gate set for both qubits and continuous variables. Furthermore, quantum computing can be performed fault tolerantly by a known scheme for encoding a qubit in an infinite-dimensional Hilbert space of a single light mode.

Figure 1

Loop-based architecture for universal quantum computing, featuring a homodyne detector (HD), displacement operation (Disp.), a phase shifter (PS) and a variable beam splitter (VBS).

Figure 2

(a) Measurement-induced squeezing gate [5]. (b) Single-loop architecture for single-mode Clifford (Gaussian) gates. (c)–(e) Procedure for an arbitrary single-mode Clifford gate. We assume that the input pulse initially arrives at the VBS at time $t=0$. (f) Programmable control sequence of system parameters. (g) Decomposition of an arbitrary $n$-mode Clifford gate [24].

Figure 3

Measurement-induced cubic phase gate in Ref. [10].