Postdoc @ LENS – University of Florence 

Wednesday June 29 – 12.00 BST

Measuring negative quasiprobabilities with a diamond spin 

One of the most fascinating issues of quantum thermodynamics is how to capture the effect of quantum coherence and quantum correlations on thermodynamic processes occurring at the nanoscale. 
This is a challenging question, because conventional methods to study energy exchange such as the two-point-measurement (TPM) scheme unavoidably destroy quantum coherence terms in the initial state [1]. A possible solution to this problem is the introduction of Kirkwood-Dirac quasiprobabilities (KDQ). Negative and/or complex values of the KDQ have been shown to imply proofs of non-classicality [2], but such values have not been observed yet in experiments. 
Here we resort to the solid-state spin platform based on optically-active NV center in diamond,  recently employed in studies on energy fluctuation relations [3-5], to demonstrate a weak-TPM protocol [6] to measure the KDQ, both in a two- and a three-level system. We also explore the possibility of implementing an interferometric scheme for the measurement of KQP and moments of their statistics, using a nuclear spin as an ancillary system. Our results represent the first experimental measurement of KDQ using a weak-TPM scheme. 

[1] M. Perarnau-Llobet, E. Bäumer, K. V. Hovhannisyan, M. Huber, A. Acin, PRL 118, 070601 (2017) 
[2] A. Levy, and M. Lostaglio, PRX Quantum 1, 010309 (2020) 
[3] S. Hernández-Gómez, S. Gherardini, F. Poggiali, F. S.Cataliotti, A. Trombettoni, P. Cappellaro, and N. Fabbri, Phys. Rev. Research 2, 023327 (2020) 
[4] S. Hernández-Gómez, N. Staudenmaier, M. Campisi, N. Fabbri, New J. Phys. 23 065004 (2021) 
[5] S. Hernández-Gómez, S. Gherardini, N. Staudenmaier, F. Poggiali, M. Campisi, A. Trombettoni, F. S. Cataliotti, P. Cappellaro 
[6] A. Belenchia, S. Gherardini, S. Hernández-Gómez, N. Fabbri,  A. Levy, M. Lostaglio, in preparation.