11,245 research outputs found
Explanation and observability of diffraction in time
Diffraction in time (DIT) is a fundamental phenomenon in quantum dynamics due
to time-dependent obstacles and slits. It is formally analogous to diffraction
of light, and is expected to play an increasing role to design coherent matter
wave sources, as in the atom laser, to analyze time-of-flight information and
emission from ultrafast pulsed excitations, and in applications of coherent
matter waves in integrated atom-optical circuits. We demonstrate that DIT
emerges robustly in quantum waves emitted by an exponentially decaying source
and provide a simple explanation of the phenomenon, as an interference of two
characteristic velocities. This allows for its controllability and
optimization.Comment: 4 pages, 6 figure
Quantum neural networks with multi-qubit potentials
We propose quantum neural networks that include multi-qubit interactions in
the neural potential leading to a reduction of the network depth without losing
approximative power. We show that the presence of multi-qubit potentials in the
quantum perceptrons enables more efficient information processing tasks such as
XOR gate implementation and prime numbers search, while it also provides a
depth reduction to construct distinct entangling quantum gates like CNOT,
Toffoli, and Fredkin. This simplification in the network architecture paves the
way to address the connectivity challenge to scale up a quantum neural network
while facilitates its training.Comment: 11 pages, 6 figure
Fast and robust spin manipulation in a quantum dot by electric fields
We apply an invariant-based inverse engineering method to control by
time-dependent electric fields electron spin dynamics in a quantum dot with
spin-orbit coupling in a weak magnetic field. The designed electric fields
provide a shortcut to adiabatic processes that flips the spin rapidly, thus
avoiding decoherence effects. This approach, being robust with respect to the
device-dependent noise, can open new possibilities for the spin-based quantum
information processing.Comment: 7 pages, 6 figures, with supplemental material. Errors in the
published version have been correcte
Pulse Control of Decoherence in a Qubit Coupled with a Quantum Environment
We study the time evolution of a qubit linearly coupled with a quantum
environment under a sequence of short pi pulses. Our attention is focused on
the case where qubit-environment interactions induce the decoherence with
population decay. We assume that the environment consists of a set of bosonic
excitations. The time evolution of the reduced density matrix for the qubit is
calculated in the presence of periodic short pi pulses. We confirm that the
decoherence is suppressed if the pulse interval is shorter than the correlation
time for qubit-environment interactions.Comment: 5 pages, 2figure
SPORT: A new sub-nanosecond time-resolved instrument to study swift heavy ion-beam induced luminescence - Application to luminescence degradation of a fast plastic scintillator
We developed a new sub-nanosecond time-resolved instrument to study the
dynamics of UV-visible luminescence under high stopping power heavy ion
irradiation. We applied our instrument, called SPORT, on a fast plastic
scintillator (BC-400) irradiated with 27-MeV Ar ions having high mean
electronic stopping power of 2.6 MeV/\mu m. As a consequence of increasing
permanent radiation damages with increasing ion fluence, our investigations
reveal a degradation of scintillation intensity together with, thanks to the
time-resolved measurement, a decrease in the decay constant of the
scintillator. This combination indicates that luminescence degradation
processes by both dynamic and static quenching, the latter mechanism being
predominant. Under such high density excitation, the scintillation
deterioration of BC-400 is significantly enhanced compared to that observed in
previous investigations, mainly performed using light ions. The observed
non-linear behaviour implies that the dose at which luminescence starts
deteriorating is not independent on particles' stopping power, thus
illustrating that the radiation hardness of plastic scintillators can be
strongly weakened under high excitation density in heavy ion environments.Comment: 5 figures, accepted in Nucl. Instrum. Methods
Measurement does not always aid state discrimination
We have investigated the problem of discriminating between nonorthogonal
quantum states with least probability of error. We have determined that the
best strategy for some sets of states is to make no measurement at all, and
simply to always assign the most commonly occurring state. Conditions which
describe such sets of states have been derived.Comment: 3 page
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