Demonstration of a Quantum Switch in a Sagnac Configuration

Teodor Strömberg (Corresponding author), Peter Schiansky, Robert W. Peterson, Marco Túlio Quintino, Philip Walther (Corresponding author)

Publications: Contribution to journalArticlePeer Reviewed


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, realizations of the quantum switch have made a trade-off between relying on optical interferometers susceptible to minute path length fluctuations and limitations on the range and fidelity of the implementable channels, thereby 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 SU(2) polarization gadget. We certify our design by successfully performing a channel discrimination task with near unity success probability.
Original languageEnglish
Article number060803
Number of pages6
JournalPhysical Review Letters
Issue number6
Publication statusPublished - 11 Aug 2023

Austrian Fields of Science 2012

  • 103025 Quantum mechanics
  • 103026 Quantum optics

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