Experimental demonstration of input-output indefiniteness in a single quantum device

Abstract

Quantum theory allows information to flow through a single device in a coherent superposition of two opposite directions, resulting into situations where the input-output direction is indefinite. Here we introduce a theoretical method to witness input-output indefiniteness in a single quantum device, and we experimentally demonstrate it by constructing a photonic setup that exhibits input-output indefiniteness with a statistical significance exceeding 69 standard deviations. Our results provide a way to characterize input-output indefiniteness as a resource for quantum information and photonic quantum technologies and enable table-top simulations of hypothetical scenarios exhibiting quantum indefiniteness in the direction of time.

5 + 18 pages, 11 figures

References in corpus (63)

• Entanglement detection
• Quantum Resource Theories
• Colloquium. Quantum Fluctuation Relations: Foundations and Applications
• Quantum correlations with no causal order
• Quantum computations without definite causal structure
• Theoretical framework for quantum networks
• Transforming quantum operations: quantum supermaps
• Experimental Superposition of Orders of Quantum Gates
• Computational advantage from quantum-controlled ordering of gates
• Experimental Verification of an Indefinite Causal Order
• Enhanced communication with the assistance of indefinite causal order
• Perfect discrimination of no-signalling channels via quantum superposition of causal structures
• Indefinite Causal Order in a Quantum Switch
• Towards Quantum Gravity: A Framework for Probabilistic Theories with Non-Fixed Causal Structure
• Exponential Communication Complexity Advantage from Quantum Superposition of the Direction of Communication
• Optimal Quantum Clocks
• Witnessing causal nonseparability
• Genralized Robustness of Entanglement
• Memory effects in quantum channel discrimination
• Closed timelike curves via post-selection: theory and experimental demonstration
• Quantum Metrology with Indefinite Causal Order
• Experimental transmission of quantum information using a superposition of causal orders
• Experimental Quantum Switching for Exponentially Superior Quantum Communication Complexity
• Quantum Operation Time Reversal
• Quantum Refrigeration with Indefinite Causal Order
• Unital Quantum Channels - Convex Structure and Revivals of Birkhoff's Theorem
• Quantum Shannon theory with superpositions of trajectories
• Multiple-time states and multiple-time measurements in quantum mechanics
• Magnetotransport of dirty-limit van Hove singularity quasiparticles
• Experimental Quantum Communication Enhancement by Superposing Trajectories
• Communication through coherent control of quantum channels
• Reversing Unknown Quantum Transformations: Universal Quantum Circuit for Inverting General Unitary Operations
• A quantum solution to the arrow-of-time dilemma
• $\pi$-Corrected Heisenberg Limit
• Strict hierarchy between parallel, sequential, and indefinite-causal-order strategies for channel discrimination
• Interference of Quantum Channels
• Optimal quantum networks and one-shot entropies
• From time-reversal symmetry to quantum Bayes' rules
• Probabilistic exact universal quantum circuits for transforming unitary operations
• Quantum and Classical Data Transmission through Completely Depolarising Channels in a Superposition of Cyclic Orders
• Operational formulation of time reversal in quantum theory
• Pre- and post-selected quantum states: density matrices, tomography, and Kraus operators
• Causal orders, quantum circuits and spacetime: distinguishing between definite and superposed causal orders
• Effective Quantum Time Travel
• The arrow of time in operational formulations of quantum theory
• Anti- (Conjugate) Linearity
• Three myths about time reversal in quantum theory
• Axioms for retrodiction: achieving time-reversal symmetry with a prior
• Optimal networks for Quantum Metrology: semidefinite programs and product rules
• Reversing Unknown Qubit-Unitary Operation, Deterministically and Exactly
• Causal structure in the presence of sectorial constraints, with application to the quantum switch
• Symmetries of quantum evolutions
• Quantum frameness for Charge-Parity-Time inversion symmetry
• Resource theory of causal connection
• Subspace preserving completely positive maps
• Optimal Probabilistic Simulation of Quantum Channels from the Future to the Past
• Gluing of completely positive maps
• Subspace local quantum channels
• Operations and single particle interferometry
• A universal quantum rewinding protocol with an arbitrarily high probability of success
• Quantum communication through devices with indefinite input-output direction
• Universal control of quantum processes using sector-preserving channels
• Inferring work by quantum superposing forward and time-reversal evolutions

Cited by in corpus (9)

• Experimental Aspects of Indefinite Causal Order in Quantum Mechanics
• Experimental superposition of time directions
• Memory in quantum processes with indefinite time direction and causal order
• Indefinite Time Directed Quantum Metrology
• Non-commutativity as a Universal Characterization for Enhanced Quantum Metrology
• Characterising transformations between quantum objects, 'completeness' of quantum properties, and transformations without a fixed causal order
• Forward-backward stochastic simulations: Q-based model for measurement and Bell-nonlocality consistent with weak local realistic premises
• Entropic uncertainty under indefinite causal order and input-output direction
• Informationally Complete Distributed Metrology Without a Shared Reference Frame