Demonstration of a quantum SWITCH in a Sagnac configuration

Abstract

The quantum SWITCH is an example of a process with an indefinite causal structure, and has attracted attention for its ability to outperform causally ordered computations within the quantum circuit model. To date, realisations of the quantum SWITCH have relied on optical interferometers susceptible to minute path length fluctuations, complicating their design, limiting their performance and posing an obstacle to extending the quantum SWITCH to multiple parties. In this Letter we overcome these limitations by demonstrating an intrinsically stable quantum SWITCH utilizing a common-path geometry facilitated by a novel reciprocal and universal $\mathrm{SU}(2)$ polarization gadget. We certify our design by successfully performing a channel discrimination task with near unity success probability.

14 pages, 10 figures, closer to the published version

References in corpus (5)

• Experimental Verification of an Indefinite Causal Order
• Strict hierarchy between parallel, sequential, and indefinite-causal-order strategies for channel discrimination
• Experimentally feasible computational advantage from quantum superposition of gate orders
• Semi-device-independent certification of indefinite causal order in a photonic quantum switch
• Demonstration of universal time-reversal for quantum processes

Cited by in corpus (10)

• Experimental Aspects of Indefinite Causal Order in Quantum Mechanics
• Higher-order Process Matrix Tomography of a passively-stable Quantum SWITCH
• Experimentally demonstrating indefinite causal order algorithms to solve the generalized Deutsch's problem
• Deterministic generation of multi-qubit entangled states among distant parties using indefinite causal order
• Indefinite Time Directed Quantum Metrology
• QuaNTUM: A Modular Quantum Communication Testbed for Scalable Fiber and Satellite Integration
• Practical implementation of arbitrary nonlocal controlled-unitary gate via indefinite causal order
• Quantum Paths: a Quantum Walk approach
• Correlations in a quantum switch-based heat engine with measurements: A proof-of-principle demonstration
• Optimal Thermalization under Indefinite Causal Order with Identical and Asymmetric Baths