Destructive Controlled-Phase Gate Using Linear Optics

TL;DR

This paper presents a new linear optics-based controlled-phase gate implementation that uses only one nonlinear sign gate, increasing success probability and suitable for applications where control qubits are destroyed.

Contribution

An alternative controlled-phase gate implementation requiring only a single nonlinear sign gate, enhancing success probability with linear optics techniques.

Findings

Higher average success probability with heralded ancilla photons

Gate implementation destroys control qubit, suitable for postselection

Simplifies controlled-phase gate construction in linear optics

Abstract

Knill, Laflamme, and Milburn [Nature 409, 46 (2001)] showed that linear optics techniques could be used to implement a nonlinear sign gate. They also showed that two of their nonlinear sign gates could be combined to implement a controlled-phase gate, which has a number of practical applications. Here we describe an alternative implementation of a controlled-phase gate that only requires the use of a single nonlinear sign gate. This gives a much higher average probability of success when the required ancilla photons are generated using heralding techniques. This implementation of a controlled-phase gate destroys the control qubit, which is acceptable in a number of applications where the control qubit would have been destroyed in any event, such as in a postselection process.