Proof, Realization, and Test of Weak Measurement on a Two or Three Qubit Computer

Thomas Radtke, S. Fritzsche

Todd A. Brun, Lajos Diósi, Walter T. Strunz

Current quantum computer technology is sufficient to realize weak measurements and the corresponding concept of ``weak values.'' We demonstrate how the weak value anomaly can be tested, along with consistency and simultaneity of weak values, using only discrete degrees of freedom. All that is needed is a quantum computer with two---or better, three---qubits. We also give an interpretation of the weak value as an effective field strength in a post-selected spin measurement.

Marco Genovese, Salvatore Virzì, Alessio Avella +11 more

Weak value measurements have been a real breakthrough in the quantum measurement framework. In particular, quantum measurements may take advantage by anomalous weak values, i.e. values out of the eigenvalues spectrum of the measured observable, both for implementing new measurement techniques and studying Quantum Mechanics foundations. In this report we show three experiments with single photons presenting anomalous weak values: the first one tests the incompatibility between quantum mechanics and noncontextual hidden variables theories, the second one is the first realization of a sequential weak value evaluation of two incompatible observables on the same photon, and the last one shows how sequential weak values can be used to test Leggett-Garg inequalities extended to multiple-measurements scenarios.

Rusko Ruskov, Alexander N. Korotkov, Ari Mizel

Lorenzo Coccia, Matteo Padovan, Andrea Pompermaier +5 more

Device-independent (DI) quantum protocols use Bell inequality violations to ensure security or certify quantum properties without assumptions on the devices’ internal workings. In this work, we study the role of rank-one qubit positive operator-valued measures (POVMs) in DI scenarios. This class includes all qubit extremal POVMs, i.e., those measurements that cannot be realized as mixtures of others, as well as part of non-extremal POVMs, recently shown to be useful in sequential quantum protocols. We demonstrate that any rank-one POVM can generate correlations in bipartite scenarios that saturate a Tsirelson inequality when two parties share an arbitrary entangled two-qubit state and perform specific self-tested measurements. For extremal POVMs, such saturation enables explicit computation of guessing probability and worst-case conditional von Neumann entropy. From the Tsirelson inequality, we establish a randomness certification method that facilitates numerical simulations and we validate it through a proof-of-concept experiment with three-outcome POVMs and tilted entangled states.

Shengjun Wu, Klaus Mølmer