74 research outputs found
Solid state optical interconnect between distant superconducting quantum chips
We propose a design for a quantum interface exploiting the electron spins in
crystals to swap the quantum states between the optical and microwave. Using
sideband driving of a superconducting flux qubit and a combined
cavity/solid-state spin ensemble Raman transition, we demonstrate how a
stimulated Raman adiabatic passage (STIRAP)-type operation can swap the quantum
state between a superconducting flux qubit and an optical cavity mode with a
fidelity higher than . We further consider two distant superconducting
qubits with their respective interfaces joined by an optical fiber and show a
quantum transfer fidelity exceeding between the two distant qubits.Comment: 5 figures, 5 page
Detection of a weak magnetic field via cavity enhanced Faraday rotation
We study the sensitive detection of a weak static magnetic field via Faraday
rotation induced by an ensemble of spins in a bimodal degenerate microwave
cavity. We determine the limit of the resolution for the sensitivity of the
magnetometry achieved using either single-photon or multiphoton inputs. For the
case of a microwave cavity containing an ensemble of Nitrogen-vacancy defects
in diamond, we obtain a magnetometry sensitivity exceeding
0.5~\text{\nano\tesla}/\sqrt{\text{\hertz}}, utilizing a single photon probe
field, while for a multiphoton input we achieve a sensitivity about 1
\text{\femto\tesla}/\sqrt{\text{\hertz}}, using a coherent probe microwave
field with power of P_\text{in}=1~\text{\nano\watt}.Comment: 8 pages, 7 figure
Optimised control of Stark-shift-chirped rapid-adiabatic-passage in a lambda-type three-level system
Inhomogeneous broadening of energy levels is one of the principal limiting
factors for achieving "slow" or "stationary" light in solid state media by
means of electromagnetically induced transparency (EIT), a quantum version of
stimulated Raman adiabatic passage (STIRAP). Stark-shift-chirped
rapid-adiabatic-passage (SCRAP) has been shown to be far less sensitive to
inhomogeneous broadening than STIRAP, a population transfer technique to which
it is closely related. We further optimise the pulses used in SCRAP to be even
less sensitive to inhomogeneous broadening in a lambda-type three-level system.
The optimised pulses perform at a higher fidelity than the standard gaussian
pulses for a wide range of detunings (i.e. large inhomogeneous broadening).Comment: 6 pages, 6 figures, 1 tabl
Quantum switching networks for perfect qubit routing
We develop the work of Christandl et al. [M. Christandl, N. Datta, T. C.
Dorlas, A. Ekert, A. Kay, and A. J. Landahl, Phys. Rev. A 71, 032312 (2005)],
to show how a d-hypercube homogenous network can be dressed by additional links
to perfectly route quantum information between any given input and output nodes
in a duration which is independent of the routing chosen and, surprisingly,
size of the network
Cavity-free nondestructive detection of a single optical photon
Detecting a single photon without absorbing it is a long standing challenge
in quantum optics. All experiments demonstrating the nondestructive detection
of a photon make use of a high quality cavity. We present a cavity free scheme
for nondestructive single-photon detection. By pumping a nonlinear medium we
implement an inter-field Rabi-oscillation which leads to a ?pi phase shift on
weak probe coherent laser field in the presence of a single signal photon
without destroying the signal photon. Our cavity-free scheme operates with a
fast intrinsic time scale in comparison with similar cavity-based schemes. We
implement a full real-space multimode numerical analysis of the interacting
photonic modes and confirm the validity of our nondestructive scheme in the
multimode case.Comment: 4 figures, 5 page
Unambiguous discrimination among oracle operators
We address the problem of unambiguous discrimination among oracle operators.
The general theory of unambiguous discrimination among unitary operators is
extended with this application in mind. We prove that entanglement with an
ancilla cannot assist any discrimination strategy for commuting unitary
operators. We also obtain a simple, practical test for the unambiguous
distinguishability of an arbitrary set of unitary operators on a given system.
Using this result, we prove that the unambiguous distinguishability criterion
is the same for both standard and minimal oracle operators. We then show that,
except in certain trivial cases, unambiguous discrimination among all standard
oracle operators corresponding to integer functions with fixed domain and range
is impossible. However, we find that it is possible to unambiguously
discriminate among the Grover oracle operators corresponding to an arbitrarily
large unsorted database. The unambiguous distinguishability of standard oracle
operators corresponding to totally indistinguishable functions, which possess a
strong form of classical indistinguishability, is analysed. We prove that these
operators are not unambiguously distinguishable for any finite set of totally
indistinguishable functions on a Boolean domain and with arbitrary fixed range.
Sets of such functions on a larger domain can have unambiguously
distinguishable standard oracle operators and we provide a complete analysis of
the simplest case, that of four functions. We also examine the possibility of
unambiguous oracle operator discrimination with multiple parallel calls and
investigate an intriguing unitary superoperator transformation between standard
and entanglement-assisted minimal oracle operators.Comment: 35 pages. Final version. To appear in J. Phys. A: Math. & Theo
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