116 research outputs found
Creating photon-number squeezed strong microwave fields by a Cooper-pair injection laser
The use of artificial atoms as an active lasing medium opens a way to
construct novel sources of nonclassical radiation. An example is the creation
of photon-number squeezed light. Here we present a design of a laser consisting
of multiple Cooper-pair transistors coupled to a microwave resonator. Over a
broad range of experimentally realizable parameters, this laser creates
photon-number squeezed microwave radiation, characterized by a Fano factor , at a very high resonator photon number. We investigate the impact of
gate-charge disorder in a Cooper-pair transistor and show that the system can
create squeezed strong microwave fields even in the presence of maximum
disorder.Comment: extended and revised version, equivalent to the published article. 11
pages, 3 figure
Non-Markovian correlation functions for open quantum systems
Beyond the conventional quantum regression theorem, a general formula for
non-Markovian correlation functions of arbitrary system operators both in the
time- and frequency-domain is given. We approach the problem by transforming
the conventional time-nonlocal master equation into dispersed time-local
equations-of-motion. The validity of our approximations is discussed and we
find that the non-Markovian terms have to be included for short times. While
calculations of the density matrix at short times suffer from the initial value
problem, a correlation function has a well defined initial state. The resulting
formula for the non-Markovian correlation function has a simple structure and
is as convenient in its application as the conventional quantum regression
theorem for the Markovian case. For illustrations, we apply our method to
investigate the spectrum of the current fluctuations of interacting quantum
dots contacted with two electrodes. The corresponding non-Markovian
characteristics are demonstrated.Comment: 11 pages, 5 figure
Pulse-controlled quantum gate sequences on a strongly coupled qubit chain
We propose a selective dynamical decoupling scheme on a chain of permanently
coupled qubits with XX type interactions, which is capable of dynamically
suppressing any coupling in the chain by applying sequences of local pulses to
the individual qubits. We demonstrate that high-fidelity single- and two-qubit
gates can be achieved by this procedure and that sequences of gates can be
implemented by this pulse control alone. We discuss the applicability and
physical limitations of our model specifically for strongly coupled
superconducting flux qubits. Since dynamically modifying the couplings between
flux qubits is challenging, they are a natural candidate for our approach.Comment: 10 pages, 7 figure
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