[Paper Review] Experimental Controlled-NOT Logic Gate for Single Photons

T. B. Pittman, Michael J. Fitch+2 more|arXiv (Cornell University)|Mar 14, 2003

Integrated Circuits and Semiconductor Failure Analysis8 citations

TL;DR

This paper demonstrates a probabilistic controlled-NOT (CNOT) quantum logic gate for single photons using linear optical elements and post-selected three-photon interference. By entangling a control photon, a target photon, and an ancilla photon, the gate achieves quantum logic operation only when all three photons are detected in specific output modes, marking a key step toward scalable linear-optical quantum computing.

ABSTRACT

We report a proof-of-principle demonstration of a probabilistic controlled-NOT gate for single photons. Single-photon control and target qubits were mixed with a single ancilla photon in a device constructed using only linear optical elements. The successful operation of the controlled-NOT gate relied on post-selected three-photon interference effects which required the detection of the photons in the output modes.

Motivation & Objective

• To realize a deterministic quantum logic gate for single photons using only linear optical components.
• To address the challenge of implementing non-linear quantum operations in photonic quantum computing with linear optics.
• To demonstrate that post-selected multi-photon interference can enable universal quantum logic gates.
• To validate the feasibility of scalable linear-optical quantum computation using probabilistic gate operations.

Proposed method

• The gate uses a network of beam splitters and phase shifters to coherently mix a control photon, a target photon, and an ancilla photon.
• The operation relies on three-photon interference effects that occur only when all three photons are detected in specific output modes.
• Post-selection is applied to the measurement outcomes to identify successful gate operations.
• The use of a single ancilla photon enables the conditional logic required for a CNOT gate.
• The system is designed to operate under the constraints of linear optics, avoiding the need for strong photon-photon interactions.
• The gate's success is heralded by the detection of all three photons in predefined output channels.

Experimental results

Research questions

• RQ1 Can a controlled-NOT gate be implemented for single photons using only linear optical elements?
• RQ2 How can post-selected multi-photon interference enable non-linear quantum logic in linear optics?
• RQ3 What role does an ancilla photon play in enabling conditional logic operations for photonic qubits?
• RQ4 Is it possible to achieve universal quantum computation with probabilistic linear-optical gates?
• RQ5 What are the limitations and success probabilities of such a gate under realistic experimental conditions?

Key findings

• The experiment successfully demonstrated a CNOT gate for single photons using only linear optical components and post-selection.
• The gate operation was confirmed through the observation of three-photon interference in the output modes.
• Successful gate operations were heralded by the detection of all three photons in specific output channels.
• The fidelity of the gate operation was limited by the probabilistic nature of the process and photon loss.
• The results validate the feasibility of using linear optics and post-selection for implementing quantum logic gates.
• The approach provides a scalable pathway toward linear-optical quantum computing, albeit with probabilistic success.