[Paper Review] Projective measurements can probe non-classical work extraction and time-correlations

Santiago Hernández-Gómez, Stefano Gherardini+4 more|arXiv (Cornell University)|Jul 26, 2022

Advanced Thermodynamics and Statistical Mechanics56 references8 citations

TL;DR

This paper demonstrates a novel experimental technique using projective measurements without ancillas to probe non-classical work extraction and time-correlations via Margenau-Hill quasiprobabilities (MHQ). By linearly combining projective measurement outcomes to cancel back-action, the authors observe work extraction peaks five times higher than standard TPM schemes and violations of classical stochastic bounds, attributed to negative MHQ values signaling quantum non-classicality.

ABSTRACT

We demonstrate an experimental technique to characterize genuinely nonclassical multi-time correlations using projective measurements with no ancillae. We implement the scheme in a nitrogen-vacancy center in diamond undergoing a unitary quantum work protocol. We reconstruct quantum-mechanical time correlations encoded in the Margenau-Hills quasiprobabilities. We observe work extraction peaks five times those of sequential projective energy measurement schemes and in violation of newly-derived stochastic bounds. We interpret the phenomenon via anomalous energy exchanges due to the underlying negativity of the quasiprobability distribution.

Motivation & Objective

• To develop an ancilla-free experimental method for probing genuine non-classical multi-time correlations in quantum processes.
• To demonstrate that projective measurements can reconstruct back-reaction-free quasiprobabilities, enabling detection of non-classical work extraction.
• To establish a framework linking negative Margenau-Hill quasiprobabilities to enhanced quantum work extraction and thermodynamic advantages.
• To provide a scalable experimental protocol using standard TPM-type measurements to witness non-classicality without weak measurements or ancillary systems.

Proposed method

• The method uses linear combinations of projective measurement outcomes to cancel measurement back-action, effectively reconstructing the quasiprobability distribution without weak interactions.
• It leverages the Margenau-Hill quasiprobability (MHQ) as a temporal correlation function derived from the Kirkwood-Dirac quasiprobability, encoding non-commutative time-ordering effects.
• The protocol is implemented on a nitrogen-vacancy (NV) center in diamond undergoing a unitary quantum work protocol with time-dependent microwave fields.
• Theoretical bounds on classical work extraction are derived and compared to experimental results to witness non-classicality.
• Numerical simulations over 10,000 random Hamiltonian parameters identify optimal conditions for negative MHQ and maximal work extraction.
• The experimental setup uses standard projective energy measurements at initial and final times, with statistical post-processing to extract MHQ and work statistics.

Experimental results

Research questions

• RQ1 Can projective measurements alone, without ancillas or weak interactions, be used to reconstruct non-classical multi-time correlations?
• RQ2 To what extent can work extraction exceed classical bounds in quantum processes, and what role does quasiprobability negativity play?
• RQ3 Can standard TPM-type measurement data be repurposed to witness non-classicality via quasiprobability analysis?
• RQ4 What Hamiltonian parameters maximize non-classical work extraction and quasiprobability negativity in a three-level system?
• RQ5 How do quantum interference terms (encoded in activities A_{if}) influence the sign and magnitude of the Margenau-Hill quasiprobability?

Key findings

• The experiment achieved work extraction peaks up to five times higher than those obtained with standard sequential projective energy measurement (TPM) schemes.
• The observed work extraction violated a newly derived classical stochastic bound, providing a witness of non-classicality in the dynamical process.
• Negative Margenau-Hill quasiprobability values were directly linked to anomalous energy exchanges and enhanced work output.
• The numerical simulations showed that setting φ₁ = φ₂ minimized the MHQ and maximized work extraction, while φ₁ ≠ φ₂ maximized quasiprobability negativity.
• The experimental data matched the theoretical predictions, with the measured work extraction and quasiprobability values falling within the predicted ranges from simulations.
• The study demonstrates that standard TPM data can be reprocessed to reveal non-classical features, enabling detection of quantum advantages without additional experimental complexity.