Quantum Metrology

Quantum metrology exploits distinctive quantum features, such as entanglement, to enhance the estimation precision of parameters governing the dynamical evolution of the probe systems beyond that achievable by classical means. This enhancement is manifested in the form of a scaling gap in precision with respect to the available resources (the number of probe systems or the average input energy) between the corresponding optimal quantum and classical strategies, and depends on the specific encoding of the parameter in the Hamiltonian describing the evolution.

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Flexible Metrology Using Cluster States

A research line that I have recently been pursuing is the question, whether architectures for measurement-based quantum computation can be employed as flexible metrology devices. In this context, we have recently investigated the possibility of creating a versatile all-purpose device for quantum metrology based on 2D cluster states [Friis, Orsucci, Skotiniotis, Sekatski, Dunjko, Briegel, Dür, New J. Phys. 19, 063044 (2017)]. We demonstrate that the quadratic scaling advantage that can be obtained in quantum parameter estimation with respect to classical strategies is maintained and can be physically realized in this new paradigm integrating quantum metrology into setups for measurement-based quantum computation. In particular, our approach allows to achieve this scaling advantage for a number of estimation scenarios that require very different probe states and measurements.

A presentation of this work can be found here (pdf).

Cluster states for metrology: Sacrificing some qubits for the preparation (green) of a probe state for sensing (purple), and some qubits for implementing optimal measurements (orange), a metrological scaling advantage in precision can be obtained for different metrology scenarios.

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Gaussian Quantum Metrology

Another research interest within quantum metrology concerns estimation scenarios where the parameter of interest is encoded in Gaussian transformations, see [Friis, Skotiniotis, Fuentes, Dür, Phys. Rev. A 92, 022106 (2015)], and more generally in the connection between quantum metrology, quantum computing and quantum thermodynamics. A pdf presentation of this work can be found here.

Parameter estimation scheme: A probe state |Ψ> is prepared, where we assume only subset k of modes can be controlled, while all other modes are prepared in the vacuum. The transformation U(ϴ) imprints the parameter ϴ on the state. A final measurement on the reduced state of the controlled modes provides information about ϴ.