2,019 research outputs found
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
Quantum walks on circles in phase space via superconducting circuit quantum electrodynamics
We show how a quantum walk can be implemented for the first time in a quantum
quincunx created via superconducting circuit quantum electrodynamics (QED), and
how interpolation from quantum to random walk is implemented by controllable
decoherence using a two resonator system. Direct control over the coin qubit is
difficult to achieve in either cavity or circuit QED, but we show that a
Hadamard coin flip can be effected via direct driving of the cavity, with the
result that the walker jumps between circles in phase space but still exhibits
quantum walk behavior over 15 steps.Comment: 8 pages, 4 figures, 2 table
Protocol for universal gates in optimally biased superconducting qubits
We present a new experimental protocol for performing universal gates in a
register of superconducting qubits coupled by fixed on-chip linear reactances.
The qubits have fixed, detuned Larmor frequencies and can remain, during the
entire gate operation, biased at their optimal working point where decoherence
due to fluctuations in control parameters is suppressed to first order.
Two-qubit gates are performed by simultaneously irradiating two qubits at their
respective Larmor frequencies with appropriate amplitude and phase, while
one-qubit gates are performed by the usual single-qubit irradiation pulses
Remote detection of aerosol pollution by ERTS
Photogrammetric and densitometric examination of ERTS-1 MSS imagery of Eastern Virginia coupled with extensive ground truth air quality and meteorological data has shown that the identification and surveying of fixed particulate emitters (smoke plumes) is feasible. A description of the ground truth network is included. The quantitative monitoring of smoke stacks from orbital altitudes over state size regions appears possible when tied to realistic plume models and minimal ground truth. Contrast reductions over urban areas can possibly be utilized to produce isopleths of particulates when supplemented by local measurements
Quantum Heating of a nonlinear resonator probed by a superconducting qubit
We measure the quantum fluctuations of a pumped nonlinear resonator, using a
superconducting artificial atom as an in-situ probe. The qubit excitation
spectrum gives access to the frequency and temperature of the intracavity field
fluctuations. These are found to be in agreement with theoretical predictions;
in particular we experimentally observe the phenomenon of quantum heating
Strong spin-photon coupling in silicon
We report the strong coupling of a single electron spin and a single
microwave photon. The electron spin is trapped in a silicon double quantum dot
and the microwave photon is stored in an on-chip high-impedance superconducting
resonator. The electric field component of the cavity photon couples directly
to the charge dipole of the electron in the double dot, and indirectly to the
electron spin, through a strong local magnetic field gradient from a nearby
micromagnet. This result opens the way to the realization of large networks of
quantum dot based spin qubit registers, removing a major roadblock to scalable
quantum computing with spin qubits
Tunable coupling of superconducting qubits
We study an LC-circuit implemented using a current-biased Josephson junction
(CBJJ) as a tunable coupler for superconducting qubits. By modulating the bias
current, the junction can be tuned in and out of resonance and entangled with
the qubits coupled to it. One can thus implement two-qubit operations by
mediating entanglement. We consider the examples of CBJJ and charge--phase
qubits. A simple recoupling scheme leads to a generalization to arbitrary qubit
designs.Comment: To appear in Phys. Rev. Lett., 3 figure
Circuit QED with a Nonlinear Resonator : ac-Stark Shift and Dephasing
We have performed spectroscopic measurements of a superconducting qubit
dispersively coupled to a nonlinear resonator driven by a pump microwave field.
Measurements of the qubit frequency shift provide a sensitive probe of the
intracavity field, yielding a precise characterization of the resonator
nonlinearity. The qubit linewidth has a complex dependence on the pump
frequency and amplitude, which is correlated with the gain of the nonlinear
resonator operated as a small-signal amplifier. The corresponding dephasing
rate is found to be close to the quantum limit in the low-gain limit of the
amplifier.Comment: Paper : 4 pages, 3 figures; Supplementary material : 1 page, 1 figur
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