Using a quantum work meter to test non-equilibrium fluctuation theorems

Non-equilibrium quantum thermodynamics is essential to describe new devices that operate far from the regime where the usual thermodynamical laws are obeyed. When quantum fluctuations dominate, defining and measuring work and heat, two central concepts in classical thermodynamics, is non-trivial. For driven, but otherwise isolated, quantum systems, work is a random variable associated with the change in the internal energy, as the first law of thermodynamics indicates. In this paper we present the design and the experimental implementation of a quantum work meter (QWM) operating on an ensemble of cold atoms. Our QWM not only directly measures work but also directly samples its probability distribution. As the work probability distribution plays a central role in the fluctuation theorems of non-equilibrium quantum thermodynamics, the QWM is an ideal tool to test their validity. In particular, we use it to verify the Jarzynski identity.