1' Circuit and lasing mechanism

1
Single-artificial-atom lasing and its suppression
by strong pumping
S. Ashhab1,2, J. R. Johansson1 , A.M.
Zagoskin1,3, and Franco Nori1,2 1Advanced
Science Institute, The Institute of Physical and
Chemical Research (RIKEN), Wako, Saitama,
Japan 2Center for Theoretical Physics, CSCS,
Department of Physics, University of Michigan,
Ann Arbor, Michigan, USA 3Department of Physics,
Loughborough University, Loughborough, UK
Summary We consider a system composed of a single
artificial atom coupled to a cavity mode. The
artificial atom is biased such that the most
dominant relaxation process in the system takes
the atom from its ground state to its excited
state, thus ensuring population inversion. Even
under this condition, lasing action can be
suppressed if the relaxation' rate, i.e. the
pumping rate, is larger than a certain threshold
value. Using simple transition-rate arguments, we
derive analytic expressions for the lasing
suppression condition and the photon-number state
of the cavity in both the lasing and
suppressed-lasing regimes.
3. Competition between emission and loss rates
1. Circuit and lasing mechanism
Emission from atom to cavity
Loss from cavity to environment
Maximum value
For small n
In the steady state
If the occupation probability has a peak in n,
the location of the peak is approximately given
by the equation
Going from (a) to (d) G is increased. The red
circle marks the most probable number of photons
in the cavity Figure (c) corresponds to the
threshold that separates the lasing and
suppressed-lasing states.
The atom is biased such that it experiences
inverted relaxation from the ground to the
excited state.
2. Simplified Hamiltonian and dissipative
processes
Jaynes-Cummings Hamiltonian
Atom
Cavity
Coupling
Thermal regime Effective temperature can be
defined
Master equation
Lasing regime

• cavity decay rate
• G atom excitation rate

Supported in part by the NSA, LPS, ARO, NSF and
JSPS. arXiv0803.1209 Corresponding author Sahel
Ashhab, ashhab_at_riken.jp