2,201 research outputs found
Competition and mergers in airline networks / 1523
Includes bibliographical references (p. 25)
Deterministic amplification of Schroedinger cat states in circuit quantum electrodynamics
We propose a dynamical scheme for deterministically amplifying photonic
Schroedinger cat states based on a set of optimal state-transfers. The scheme
can be implemented in strongly coupled qubit-cavity systems and is well suited
to the capabilities of state of the art superconducting circuits. The ideal
analytical scheme is compared with a full simulation of the open
Jaynes-Cummings model with realistic device parameters. This amplification tool
can be utilized for practical quantum information processing in non-classical
continuous-variable states.Comment: A revised manuscript has 6 figure
Engineering entanglement for metrology with rotating matter waves
Entangled states of rotating, trapped ultracold bosons form a very promising scenario for quantum metrology. In order to employ such states for metrology, it is vital to understand their detailed form and the enhanced accuracy with which they could measure phase, in this case generated through rotation. In this work, we study the rotation of ultracold bosons in an asymmetric trapping potential beyond the lowest Landau level (LLL) approximation. We demonstrate that while the LLL can identify reasonably the critical frequency for a quantum phase transition and entangled state generation, it is vital to go beyond the LLL to identify the details of the state and quantify the quantum Fisher information (which bounds the accuracy of the phase measurement). We thus identify a new parameter regime for useful entangled state generation, amenable to experimental investigation
Weak nonlinearities: A new route to optical quantum computation
Quantum information processing (QIP) offers the promise of being able to do
things that we cannot do with conventional technology. Here we present a new
route for distributed optical QIP, based on generalized quantum non-demolition
measurements, providing a unified approach for quantum communication and
computing. Interactions between photons are generated using weak
non-linearities and intense laser fields--the use of such fields provides for
robust distribution of quantum information. Our approach requires only a
practical set of resources, and it uses these very efficiently. Thus it
promises to be extremely useful for the first quantum technologies, based on
scarce resources. Furthermore, in the longer term this approach provides both
options and scalability for efficient many-qubit QIP.Comment: 7 Pages, 4 Figure
Overcoming decoherence in the collapse and revival of spin Schr\"odinger cats
In addition to being a very interesting quantum phenomenon, Schr\"odinger cat
swapping has the potential for application in the preparation of quantum states
that could be used in metrology and other quantum processing. We study in
detail the effects of field decoherence on a cat-swapping system comprising a
set of identical qubits, or spins, all coupled to a field mode. We demonstrate
that increasing the number of spins actually mitigates the effects of field
decoherence on the collapse and revival of a spin Schr\"odinger cat, which
could be of significant utility in quantum metrology and other quantum
processing.Comment: 4 pages, 2 figure
The efficiencies of generating cluster states with weak non-linearities
We propose a scalable approach to building cluster states of matter qubits
using coherent states of light. Recent work on the subject relies on the use of
single photonic qubits in the measurement process. These schemes can be made
robust to detector loss, spontaneous emission and cavity mismatching but as a
consequence the overhead costs grow rapidly, in particular when considering
single photon loss. In contrast, our approach uses continuous variables and
highly efficient homodyne measurements. We present a two-qubit scheme, with a
simple bucket measurement system yielding an entangling operation with success
probability 1/2. Then we extend this to a three-qubit interaction, increasing
this probability to 3/4. We discuss the important issues of the overhead cost
and the time scaling. This leads to a "no-measurement" approach to building
cluster states, making use of geometric phases in phase space.Comment: 21 pages, to appear in special issue of New J. Phys. on
"Measurement-Based Quantum Information Processing
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