Abstract

Self-testing is a method to infer the underlying physics of a quantum experiment in a black box scenario. As such it represents the strongest form of certification for quantum systems. In recent years a considerable self-testing literature has developed, leading to progress in related device-independent quantum information protocols and deepening our understanding of quantum correlations. In this work we give a thorough and self-contained introduction and review of self-testing and its application to other areas of quantum information.

Highlights

  • In contrast to classical theories, states in quantum physics can be entangled and sets of measurements can be incompatible

  • The outcomes of incompatible measurements made on the local subsystems of an entangled quantum state can exhibit correlations that are provably stronger than any resulting from a classical theory, a phenomenon known as Bell nonlocality

  • These works have since given birth to the field of self-testing, which broadly speaking aims to understand the structure of the set of quantum correlations and identify those correlations that admit a unique physical realisation

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Summary

Introduction

In contrast to classical theories, states in quantum physics can be entangled and sets of measurements can be incompatible. As more was understood about Bell nonlocality, a number of works [SW87, PR92, BMR92, Tsi93] eventually pointed out that there exist Bell nonlocal correlations that—as well as requiring entanglement and incompatibility—can only be produced by making particular sets of incompatible measurements on particular entangled states These works have since given birth to the field of self-testing, which broadly speaking aims to understand the structure of the set of quantum correlations and identify those correlations that admit a unique physical realisation. A similar idea was already present in [MY98] in a cryptographic context, using the term ‘self-checking’ instead of ‘self-testing’ These early works introduced the paradigm of device-independence, to which self-testing is intimately related. We recommend [McK10, Kan, Kan16] as valuable texts for first time readers

Self-testing as a device-independent protocol
Notation
The self-testing scenario
Self-testing of states
Self-testing of measurements
Robust self-testing
Extractability relative to a Bell inequality
The issue of complex conjugation
Self-testing via simulation
Measurement self-testing based on commutation
A first example
Geometrical proof of anticommutativity
Algebraic proof of anticommutativity
Swap gate
Partial vs full Swap gates
Self-testing of bipartite states
The maximally entangled pair of qubits
Self-testing of partially entangled states
Self-testing of qudit states
Subspace methods
Self-testing from qudit correlations
Group theoretic tools
Self-testing n maximally entangled pairs of qubits
Sequential self-testing
Parallel self-testing
Overlapping qubits
Self-testing of multipartite states
Self-testing of graph states from stabilizer operators
Tailoring Bell inequalities
Reductions to bipartite methods
Parallel self-testing of multipartite states
Self-testing using only marginal information
Robust self-testing of states
Norm inequalities method
Utilising Jordan’s lemma
Operator inequalities method
Numerical Swap method
Algebraic method
Robust certification of large entanglement
Qudit measurements
Qubit measurements
Non-projective measurements
Phase kickback method for self-testing complex measurements
Self-testing measurements based on commutation
Post-hoc self-testing of measurements
Self-testing of entangling measurements
Robust measurement self-testing
Extensions of self-testing to other scenarios
Self-testing of quantum gates and circuits
Semi-device-independent scenarios
Self-testing in the prepare-and-measure scenario
Self-testing through noncontextuality inequalities
10 Applications of self-testing
10.1 Device-independent randomness generation
10.2.1 Quantum key distribution
10.2.2 Cryptography beyond quantum key distribution
10.3 Entanglement detection
10.4 Delegated quantum computing
10.5.1 Correlations from finite vs infinite dimensional quantum strategies
10.5.2 Uncertainty relations and Bell nonlocality
11 Experiments
12 Concluding remarks and open questions
Self-testing complex measurements
Regularisation trick
Swap isometries
Localising matrices in the Swap method
B State and measurement assumptions
Findings
Measurements
Full Text
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