Experimental Quantum Key Distribution in an Indefinite Causal Order

• URL: http://arxiv.org/abs/2608.13561v1
• Date: Thu, 13 Aug 2026 17:59:58 GMT
• Title: Experimental Quantum Key Distribution in an Indefinite Causal Order
• Abstract summary: Experimental implementation of BB84-like quantum cryptography by placing Alice and Bob's measurement-and-preparation operations in a photonic quantum SWITCH.<n>Average eavesdropper detection probability of $0.15 pm 0.02$ per shared qubit.<n>Experiment relies on a new measurement technique that allows the polarization of a photon to be measured inside the quantum SWITCH without destroying path coherence.
• Score: 0.0
• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: In quantum physics the order in which different operations occur can be placed in superposition. The resulting processes have an indefinite causal order and are both of fundamental interest and can be viewed as a novel quantum resource that enables a variety of new protocols. Here we report an experimental implementation of one such protocol, where we perform BB84-like quantum cryptography by placing Alice and Bob's measurement-and-preparation operations in a photonic quantum SWITCH. By embedding Alice and Bob within the quantum SWITCH, the protocol achieves an average eavesdropper detection probability of $0.15 \pm 0.02$ per shared qubit, with eavesdropper detection performed through measurements of the control qubit rather than by comparing the key. Unlike the standard BB84 and related schemes, which detect eavesdropping by publicly revealing and discarding a fraction of the raw key, our approach requires no disclosure of key material: every retained qubit can, in principle, be tested for eavesdropping while remaining available for key generation. The experiment relies on a new measurement technique that allows the polarization of a photon to be measured inside the quantum SWITCH without destroying path coherence. Although the present implementation does not yet constitute a secure quantum key distribution protocol, owing to the post-selection required for measurements within the quantum SWITCH, it provides a proof of principle that indefinite causal order can be exploited to detect eavesdropping without sacrificing key bits.

Related papers

• Self-Sifting quantum key distribution [0.0]
  We introduce a novel two-way quantum key distribution protocol in which the sender and receiver employ one qubit of a maximally entangled Bell state as the quantum channel for key exchange.<n>Unlike conventional two-way QKD protocols, all sifting operations and eavesdropper detection procedures are postponed until the completion of the quantum communication stage.<n>We analyze a broad class of ancilla-based attacks, in which an eavesdropper couples an ancillary system to the transmitted qubit in an attempt to gain information about the key.
  arXiv  Detail & Related papers  (2026-06-25T17:17:12Z)
• Certifying coherence in quantum devices under classical control [33.72751145910978]
  We prove that coherence can be fully characterised through a hierarchy of semidefinite programs.<n>For the important special case of qubits, we exploit conceptual connections with the theory of joint measurability.<n>We apply these methods to determine whether quantum channels are able to preserve coherence or are inherently coherence-breaking.
  arXiv  Detail & Related papers  (2026-06-02T14:20:45Z)
• Quantum Internet in a Nutshell -- Advancing Quantum Communication with Ion Traps [25.519081784735068]
  We study the incorporation of small quantum error correction codes into quantum communication protocols.<n>We find that these codes can help to suppress the noise level and to monitor the noise profile of the channel.
  arXiv  Detail & Related papers  (2025-07-18T22:07:54Z)
• Decoherence-assisted quantum key distribution [37.69303106863453]
  We show that our method reduces the amount of information that an eavesdropper can obtain in the BB84 protocol under the entangling probe attack. We demonstrate experimentally that Alice and Bob can agree on a scheme to that gives low values of the quantum bit error rate.
  arXiv  Detail & Related papers  (2024-05-30T15:28:07Z)
• Single-Round Proofs of Quantumness from Knowledge Assumptions [41.94295877935867]
  A proof of quantumness is an efficiently verifiable interactive test that an efficient quantum computer can pass. Existing single-round protocols require large quantum circuits, whereas multi-round ones use smaller circuits but require experimentally challenging mid-circuit measurements. We construct efficient single-round proofs of quantumness based on existing knowledge assumptions.
  arXiv  Detail & Related papers  (2024-05-24T17:33:10Z)
• The Quantum Cryptography Approach: Unleashing the Potential of Quantum Key Reconciliation Protocol for Secure Communication [7.318072482453136]
  Quantum Key Distribution (QKD) has been recognized as the most important breakthrough in quantum cryptography. This paper proposes a novel method that allows users to communicate while generating the secure keys and securing the transmission without any leakage of the data.
  arXiv  Detail & Related papers  (2024-01-17T05:41:17Z)
• Secure Key from Quantum Discord [22.97866257572447]
  We show how to make use of discord to analyze security in a specific quantum cryptography protocol. Our method is robust against imperfections in qubit sources and qubit measurements as well as basis misalignment due to quantum channels.
  arXiv  Detail & Related papers  (2023-04-12T14:21:49Z)
• Simple Tests of Quantumness Also Certify Qubits [69.96668065491183]
  A test of quantumness is a protocol that allows a classical verifier to certify (only) that a prover is not classical. We show that tests of quantumness that follow a certain template, which captures recent proposals such as (Kalai et al., 2022) can in fact do much more. Namely, the same protocols can be used for certifying a qubit, a building-block that stands at the heart of applications such as certifiable randomness and classical delegation of quantum computation.
  arXiv  Detail & Related papers  (2023-03-02T14:18:17Z)
• Interactive Protocols for Classically-Verifiable Quantum Advantage [46.093185827838035]
  "Interactions" between a prover and a verifier can bridge the gap between verifiability and implementation. We demonstrate the first implementation of an interactive quantum advantage protocol, using an ion trap quantum computer.
  arXiv  Detail & Related papers  (2021-12-09T19:00:00Z)
• Eavesdropping a Quantum Key Distribution network using sequential quantum unsharp measurement attacks [0.8010615606748019]
  We consider a pure two-qubit state shared between two parties Alice and Bob, sharing quantum steerable correlations. One qubit of the shared state is with Alice and the other one while going to the Bob's place is intercepted by multiple sequential eavesdroppers.
  arXiv  Detail & Related papers  (2021-08-23T19:10:33Z)
• Experimental characterisation of unsharp qubit observables and sequential measurement incompatibility via quantum random access codes [0.0]
  We report an experimental implementation of unsharp qubit measurements in a sequential communication protocol. The protocol involves three parties; the first party prepares a qubit system, the second party performs operations which return a classical and quantum outcome, and the latter is measured by the third party.
  arXiv  Detail & Related papers  (2020-01-14T13:37:04Z)

This list is automatically generated from the titles and abstracts of the papers in this site.

This site does not guarantee the quality of this site (including all information) and is not responsible for any consequences.