Alladi Ramakrishnan Hall

Role of coupling and prior information in quantum heat engines

George Thomas

IISER--Mohali

Quantum thermodynamic machines are novel tools to understand the
thermodynamic behaviour of quantum systems. We studied two spin-1/2
systems, coupled via isotropic Heisenberg interaction as the working medium
for a quantum Otto cycle [1]. In the four-staged cycle, the adiabatic
processes are done by changing the external magnetic field. Some
interesting observations are pointed out such as the efficiency of the
coupled model is higher than that of the uncoupled model, apparent flow of
heat from the cold bath to the hot bath in the local description of the
spins, and the total work as the sum of the local contributions. An upper
bound for the efficiency is derived which is shown to be tighter than the
Carnot bound. Frictional effect observed in the heat engine due to
inhomogeneous driving of the spins is also discussed [2]. This effect
arises when the non-commutativity of the internal and the external
Hamiltonian leads to the non-commutativity of the total Hamiltonian at
different instances during the driving [3]. We also study the reduction in
the useful work and the entropy production with respect to the time
allocated for the adiabatic branches of the heat cycle. As two extreme
cases, a slow driving where the quantum adiabatic theorem holds and a
sudden process where the density matrix remains unchanged are also
discussed. Further, we discuss a quantum model of heat engine, where the
intrinsic energy scales are uncertain [4,5]. Based on the prior
information, we assign a prior probability distribution for the uncertain
parameter. Using this prior distribution, we estimate the expected
behaviour of the heat engine.


1. G. Thomas and R. S. Johal, Phys. Rev. E 83, 031135(2011).

2. G. Thomas and R. S. Johal, Eur. Phys. J. B 87:166 (2014).

3. R. Kosloff and T. Feldmann, Phys. Rev. E 65, 055102(R) (2002).

4. R. S. Johal, Phys. Rev. E 82, 061113 (2010).

5. G. Thomas and R. S. Johal, Phys. Rev. E 85, 041146 (2012).