I am going to post here all newly submitted articles on the arXiv related to superconducting circuits. If your article has been accidentally forgotten, feel free to contact me
14
Aug
2012
Controlled catch and release of microwave photon states
, in which the resonant
cavity confines photons and promotes"]strong light-matter interactions. The
cavity end-mirrors determine the performance of the coupled system, with higher
mirror reflectivity yielding better quantum coherence, but higher mirror
transparency giving improved measurement and control, forcing a compromise. An
alternative is to control the mirror transparency, enabling switching between
long photon lifetime during quantum interactions and large signal strength when
performing measurements. Here we demonstrate the superconducting analogue,
using a quantum system comprising a resonator and a qubit, with variable
coupling to a measurement transmission line. The coupling can be adjusted
through zero to a photon emission rate 1,000 times the intrinsic photon decay
rate. We use this system to control photons in coherent states as well as in
non-classical Fock states, and dynamically shape the waveform of released
photons. This has direct applications to circuit quantum electrodynamics [3],
and may enable high-fidelity quantum state transfer between distant qubits, for
which precisely-controlled waveform shaping is a critical and non-trivial
requirement [4, 5].
Nonlinear Optics Quantum Computing with Circuit-QED
One approach to quantum information processing is to use photons as quantum
bits and rely on linear optical elements for most operations. However, some
optical nonlinearity is necessary
to enable universal quantum computing. Here,
we suggest a circuit-QED approach to nonlinear optics quantum computing in the
microwave regime, including a deterministic two-photon phase gate. Our specific
example uses a hybrid quantum system comprising a LC resonator coupled to a
superconducting flux qubit to implement a nonlinear coupling. Compared to the
self-Kerr nonlinearity, we find that our approach has improved tolerance to
noise in the qubit while maintaining fast operation.
12
Aug
2012
Direct Wigner tomography of a superconducting anharmonic oscillator
The analysis of wave-packet dynamics may be greatly simplified when viewed in
phase-space. While harmonic oscillators are often used as a convenient platform
to study wave-packets,
arbitrary state preparation in these systems is more
challenging. Here, we demonstrate a direct measurement of the Wigner
distribution of complex photon states in an anharmonic oscillator – a
superconducting phase circuit, biased in the small anharmonicity regime. We
test our method on both non-classical states composed of two energy eigenstates
and on the dynamics of a phase-locked wavepacket. This method requires a simple
calibration, and is easily applicable in our system out to the fifth level.
09
Aug
2012
First-order sidebands in circuit QED using qubit frequency modulation
Sideband transitions have been shown to generate controllable interaction
between superconducting qubits and microwave resonators. Up to now, these
transitions have been implemented
with voltage drives on the qubit or the
resonator, with the significant disadvantage that such implementations only
lead to second-order sideband transitions. Here we propose an approach to
achieve first-order sideband transitions by relying on controlled oscillations
of the qubit frequency using a flux-bias line. Not only can first-order
transitions be significantly faster, but the same technique can be employed to
implement other tunable qubit-resonator and qubit-qubit interactions. We
discuss in detail how such first-order sideband transitions can be used to
implement a high fidelity controlled-NOT operation between two transmons
coupled to the same resonator.
07
Aug
2012
Observing the Nonequilibrium Dynamics of the Quantum Transverse-Field Ising Chain in Circuit QED
We show how a quantum Ising spin chain in a time-dependent transverse
magnetic field can be simulated and experimentally probed in the framework of
circuit QED with current technology.
The proposed setup provides a new platform
for observing the nonequilibrium dynamics of interacting many-body systems. We
calculate its spectrum to offer a guideline for its initial experimental
characterization. We demonstrate that quench dynamics and the propagation of
localized excitations can be observed with the proposed setup and discuss
further possible applications and modifications of this circuit QED quantum
simulator.
01
Aug
2012
Many Body Physics with Coupled Transmission Line Resonators
We present the Josephson junction intersected superconducting transmission
line resonator. In contrast to the Josephson parametric amplifier, Josephson
bifurcation amplifier and Josephson
parametric converter we consider the regime
of few microwave photons. We review the derivation of eigenmode frequencies and
zero point fluctuations of the nonlinear transmission line resonator and the
derivation of the eigenmode Kerr nonlinearities. Remarkably these
nonlinearities can reach values comparable to Transmon qubits rendering the
device ideal for accessing the strongly correlated regime. This is particularly
interesting for investigation of quantum many-body dynamics of interacting
particles under the influence of drive and dissipation. We provide current
profiles for the device modes and investigate the coupling between resonators
in a network of nonlinear transmission line resonators.
Inelastic Microwave Photon Scattering off a Quantum Impurity in a Josephson-Junction Array
Quantum fluctuations in an anharmonic superconducting circuit enable
frequency conversion of individual incoming photons. This effect, linear in the
photon beam intensity, leads to
ramifications for the standard input-output
circuit theory. We consider an extreme case of anharmonicity in which photons
scatter off a small set of weak links within a Josephson junction array. We
show that this quantum impurity displays Kondo physics and evaluate the elastic
and inelastic photon scattering cross sections. These cross sections reveal
many-body properties of the Kondo problem that are hard to access in its
traditional fermionic version.
19
Jul
2012
Nonlinear oscillators and high fidelity qubit state measurement in circuit quantum electrodynamics
In this book chapter we analyze the high excitation nonlinear response of the
Jaynes-Cummings model in quantum optics when the qubit and cavity are strongly
coupled. We focus on the
parameter ranges appropriate for transmon qubits in
the circuit quantum electrodynamics architecture, where the system behaves
essentially as a nonlinear quantum oscillator and we analyze the quantum and
semi-classical dynamics. One of the central motivations is that under strong
excitation tones, the nonlinear response can lead to qubit quantum state
discrimination and we present initial results for the cases when the qubit and
cavity are on resonance or far off-resonance (dispersive).
18
Jul
2012
Realization of GHz-frequency impedance matching circuits for nano-scale devices
Integrating nano-scale objects, such as single molecules or carbon nanotubes,
into impedance transformers and performing radio-frequency measurements allows
for high time-resolution
transport measurements with improved signal-to-noise
ratios. The realization of such transformers implemented with superconducting
transmission lines for the 2-10 GHz frequency range is presented here.
Controlled electromigration of an integrated gold break junction is used to
characterize a 6 GHz impedance matching device. The real part of the RF
impedance of the break junction extracted from microwave reflectometry at a
maximum bandwidth of 45 MHz of the matching circuit is in good agreement with
the measured direct current resistance.
14
Jul
2012
Tunable coupling engineering between superconducting resonators: from sidebands to effective gauge fields
In this work we show that a tunable coupling between microwave resonators can
be engineered by means of simple Josephson junctions circuits, such as dc- and
rf-SQUIDs. We show that
by controlling the time dependence of the coupling it
is possible to switch on and off and modulate the cross-talk, boost the
interaction towards the ultrastrong regime, as well as to engineer red and blue
sideband couplings, nonlinear photon hopping and classical gauge fields. We
discuss how these dynamically tunable superconducting circuits enable key
applications in the fields of all optical quantum computing, continuous
variable quantum information and quantum simulation – all within the reach of
state of the art in circuit-QED experiments.