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
13
Dez
2012
Realizing an $n$-target-qubit controlled phase gate in cavity QED: An approach without classical pulses
We propose a way to realize a multiqubit controlled phase gate with one qubit
simultaneously controlling $n$ target qubits using atoms in cavity QED. In this
proposal, there is no need
of using classical pulses during the entire gate
operation. The gate operation time scales as $sqrt{n}$ only and thus the gate
can be performed faster when compared with sending atoms through the cavity one
at a time. In addition, only three steps of operations are required for
realizing this $n$-target-qubit controlled phase gate. This proposal is quite
general, which can be applied to other physical systems such as various
superconducting qubits coupled to a resonator, NV centers coupled to a
microsphere cavity or quantum dots in cavity QED.
12
Dez
2012
Anisotropic rare-earth spin ensemble strongly coupled to a superconducting resonator
Interfacing photonic and solid-state qubits within a hybrid quantum
architecture offers a promising route towards large scale distributed quantum
computing. Ideal candidates for coherent
qubit interconversion are optically
active spins magnetically coupled to a superconducting resonator. We report on
a cavity QED experiment with magnetically anisotropic Er3+:Y2SiO5 crystals and
demonstrate strong coupling of rare-earth spins to a lumped element resonator.
In addition, the electron spin resonance and relaxation dynamics of the erbium
spins are detected via direct microwave absorption, without aid of a cavity.
Coupling mechanism between microscopic two-level system and superconducting qubits
We propose a scheme to clarify the coupling nature between superconducting
Josephson qubits andmicroscopic two-level systems. Although dominant interest
in studying two-level systems
was in phase qubits previously, we find that the
sensitivity of the generally used spectral method in phase qubits is not
sufficient to evaluate the exact form of the coupling. On the contrary, our
numerical calculation shows that the coupling strength changes remarkably with
the flux bias for a flux qubit, providing a useful tool to investigate the
coupling mechanism between the two-level systems and qubits.
11
Dez
2012
Three qubit Grover’s algorithm using superconducting quantum interference devices in cavity QED
We present a scheme for the implementation of three qubit Grover’s algorithm
using four-level superconducting quantum interference devices (SQUIDs) coupled
to a superconducting
resonator. The scheme is based on resonant, off-resonant
interaction of the cavity field with SQUIDs and the application of classical
microwave pulses. We show that adjustment of SQUID level spacing during the
gate operations, adiabatic passage, and second-order detuning are not required
that leads to faster implementation. We also show that the marked state can be
searched with high fidelity even in the presence of level decay and cavity
dissipation.
Processing Quantum Information in Hybrid Topological Qubit and Superconducting Flux Qubit System
A composite system of Majorana-hosted semiconductor nanowire and
superconducting flux qubit is inves- tigated. It is found that the coupling
between these two subsystems can be controlled
electrically, supplying a
convenient method to implement {pi}/8 phase gate of a Majorana-based
topological qubit. We also present a scheme to transfer information from the
flux qubit to the topological qubit using Landau-Zener transition. In addition,
a structure named top-flux-flux is proposed to retrieve the information stored
in the topological qubit. With the demonstration of the entanglement of two
topological qubits, it is very promising to do quantum information process with
this hybrid system.
10
Dez
2012
Circuit QED lattices: towards quantum simulation with superconducting circuits
The Jaynes-Cummings model describes the coupling between photons and a single
two-level atom in a simplified representation of light-matter interactions. In
circuit QED, this model
is implemented by combining microwave resonators and
superconducting qubits on a microchip with unprecedented experimental control.
Arranging qubits and resonators in the form of a lattice realizes a new kind of
Hubbard model, the Jaynes-Cummings-Hubbard model, in which the elementary
excitations are polariton quasi-particles. Due to the genuine openness of
photonic systems, circuit QED lattices offer the possibility to study the
intricate interplay of collective behavior, strong correlations and
non-equilibrium physics. Thus, turning circuit QED into an architecture for
quantum simulation, i.e., using a well-controlled system to mimic the intricate
quantum behavior of another system too daunting for a theorist to tackle
head-on, is an exciting idea which has served as theorists‘ playground for a
while and is now also starting to catch on in experiments. This review gives a
summary of the most recent theoretical proposals and experimental efforts in
this context.
Full coherent frequency conversion between two microwave propagating modes
We demonstrate full frequency conversion in the microwave domain using a
Josephson three-wave mixing device pumped at the difference between the
frequencies of its fundamental eigenmodes.
By measuring the signal output as a
function of the intensity and phase of the three input signal, idler and pump
tones, we show that the device functions as a controllable three-wave
beam-splitter/combiner for propagating microwave modes, in accordance with
theory. Losses at the full conversion point are found to be less than 10^-2.
Potential applications of the device include quantum information transduction
and realization of an ultra-sensitive interferometer with controllable
feedback.
07
Dez
2012
Experimental signature of programmable quantum annealing
Quantum annealing is a general strategy for solving difficult optimization
problems with the aid of quantum adiabatic evolution. Both analytical and
numerical evidence suggests that
under idealized, closed system conditions,
quantum annealing can outperform classical thermalization-based algorithms such
as simulated annealing. Do engineered quantum annealing devices effectively
perform classical thermalization when coupled to a decohering thermal
environment? To address this we establish, using superconducting flux qubits
with programmable spin-spin couplings, an experimental signature which is
consistent with quantum annealing, and at the same time inconsistent with
classical thermalization, in spite of a decoherence timescale which is orders
of magnitude shorter than the adiabatic evolution time. This suggests that
programmable quantum devices, scalable with current superconducting technology,
implement quantum annealing with a surprising robustness against noise and
imperfections.
23
Nov
2012
Relativistic Quantum Teleportation with superconducting circuits
We study the effects of relativistic motion on quantum teleportation and
propose a realizable experiment where our results can be tested. We compute
bounds on the optimal fidelity of
teleportation when one of the observers
undergoes non-uniform motion for a finite time. The upper bound to the optimal
fidelity is degraded due to the observer’s motion however, we discuss how this
degradation can be corrected. These effects are observable for experimental
parameters that are within reach of cutting-edge superconducting technology.
19
Nov
2012
Non-locally entangled microwave and micromechanical squeezed cats: a phase transition-based protocol
Electromechanical systems currently offer a path to engineering quantum
states of microwave and micromechanical modes that are of both fundamental and
applied interest. Particularly
desirable, but not yet observed, are mechanical
states that exhibit entanglement, wherein non-classical correlations exist
between distinct modes; squeezing, wherein the quantum uncertainty of an
observable quantity is reduced below the standard quantum limit; and
Schr“odinger cats, wherein a single mode is cast in a quantum superposition of
macroscopically distinct classical states. Also, while most investigations of
electromechanical systems have focussed on single- or few-body scenarios, the
many-body regime remains virtually unexplored. In such a regime quantum phase
transitions naturally present themselves as a resource for quantum state
generation, thereby providing a route toward entangling a large number of
electromechanical systems in highly non-classical states. Here we show how to
use existing superconducting circuit technology to implement a (quasi) quantum
phase transition in an array of electromechanical systems such that
entanglement, squeezing, and Schr“odinger cats become simultaneously
observable across multiple microwave and micromechanical oscillators.