3,264 research outputs found
A superconducting qubit with Purcell protection and tunable coupling
We present a superconducting qubit for the circuit quantum electrodynamics
architecture that has a tunable coupling strength g. We show that this coupling
strength can be tuned from zero to values that are comparable with other
superconducting qubits. At g = 0 the qubit is in a decoherence free subspace
with respect to spontaneous emission induced by the Purcell effect. Furthermore
we show that in the decoherence free subspace the state of the qubit can still
be measured by either a dispersive shift on the resonance frequency of the
resonator or by a cycling-type measurement.Comment: 4 pages, 3 figure
Signatures of Hong-Ou-Mandel Interference at Microwave Frequencies
Two-photon quantum interference at a beam splitter, commonly known as
Hong-Ou-Mandel interference, was recently demonstrated with
\emph{microwave-frequency} photons by Lang \emph{et
al.}\,\cite{lang:microwaveHOM}. This experiment employed circuit QED systems as
sources of microwave photons, and was based on the measurement of second-order
cross-correlation and auto-correlation functions of the microwave fields at the
outputs of the beam splitter. Here we present the calculation of these
correlation functions for the cases of inputs corresponding to: (i) trains of
\emph{pulsed} Gaussian or Lorentzian single microwave photons, and (ii)
resonant fluorescent microwave fields from \emph{continuously-driven} circuit
QED systems. The calculations include the effects of the finite bandwidth of
the detection scheme. In both cases, the signature of two-photon quantum
interference is a suppression of the second-order cross-correlation function
for small delays. The experiment described in Ref.
\onlinecite{lang:microwaveHOM} was performed with trains of \emph{Lorentzian}
single photons, and very good agreement between the calculations and the
experimental data was obtained.Comment: 11 pages, 3 figure
Alien Registration- Blais, Rose A. (Lewiston, Androscoggin County)
https://digitalmaine.com/alien_docs/30729/thumbnail.jp
Alien Registration- Blais, Rose A. (Lewiston, Androscoggin County)
https://digitalmaine.com/alien_docs/30729/thumbnail.jp
Alien Registration- Blais, Marie A. (Lewiston, Androscoggin County)
https://digitalmaine.com/alien_docs/30723/thumbnail.jp
Heisenberg-limited qubit readout with two-mode squeezed light
We show how to use two-mode squeezed light to exponentially enhance
cavity-based dispersive qubit measurement. Our scheme enables true
Heisenberg-limited scaling of the measurement, and crucially, is not restricted
to small dispersive couplings or unrealistically long measurement times. It
involves coupling a qubit dispersively to two cavities, and making use of a
symmetry in the dynamics of joint cavity quadratures (a so-called
quantum-mechanics-free subsystem). We discuss the basic scaling of the scheme
and its robustness against imperfections, as well as a realistic implementation
in circuit quantum electrodynamics.Comment: 5 pages, 4 figures, Supplemental Materia
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