IWNET12
IWNET12
Quantum heat engines: A thermodynamic study
Upendra Harbola1
1 Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore, India
Abstract
Devices, such as solar cells, lasers, and photosynthesis cells, where quantum coherence is involved in their
operation, are known as quantum heat engines (QHE). Quantum eects in such systems can reveal themselves
in many curious ways, defying our common sense. Lasing without population inversion [1], extracting work
from a single thermal bath[2], electromagnetically induced transparency[3], and several other eects have been
demonstrated by the proper manipulation of quantum coherences. One of the most interesting properties of
a heat engine is its eciency which is dened as the ratio of the work performed to the absorbed heat. The
maximum eciency of a classical heat engine working between two temperatures Th and Tc < (Th) is given
by the Carnot's eciency, ηc = 1 − Tc/Th. This is reached when the work is done in an adiabatic manner
(quasi-equilibrium) where the corresponding power is zero. This renders a Carnot engine impractical. A useful
characterization of heat engines is obtained by maximizing the power output with respect to controllable set of
parameters and then studying their eciency.
In this talk, I will discuss the output power and the eciency of a quantum heat engine that converts incoherent
thermal energy into coherent cavity photons, which is the useful work. In the heat engine operating at maximum
power, the output power and the corresponding eciency are strongly inuenced by quantum eects, which
become increasingly important as the photon occupation in the cavity mode is decreased. As the system size
decreases, uctuations start to play a signicant role. Recently there has been a renewed interest in studying
uctuations in systems driven far from equilibrium. I will talk about some recent theoretical developments to
study uctuations in nonequilibrium quantum systems. Some applications to the quantum heat engine will be
discussed.
References
[1] S.Ya. Kilin, K. T. Kapale, and M. O. Scully, Phys. Rev. Lett. 100, 173609 (2008).
[2] M. O. Scully, M. S. Zubairy, G. S. Agarwal and H. Walther, Science 299, 862 (2003).
[3] S. E. Harris, Physics Today, 50 (7), 36 (1997).
E-mail: uharbola@ipc.iisc.ernet.in

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