49,257 research outputs found
Magnon dark modes and gradient memory
Extensive efforts have been expended in developing hybrid quantum systems to
overcome the short coherence time of superconducting circuits by introducing
the naturally long-lived spin degree of freedom. Among all the possible
materials, single-crystal yttrium iron garnet has shown up very recently as a
promising candidate for hybrid systems, and various highly coherent
interactions, including strong and even ultra-strong coupling, have been
demonstrated. One distinct advantage of these systems is that the spins are in
the form of well-defined magnon modes, which allows flexible and precise
tuning. Here we demonstrate that by dissipation engineering, a non-Markovian
interaction dynamics between the magnon and the microwave cavity photon can be
achieved. Such a process enables us to build a magnon gradient memory to store
information in the magnon dark modes, which decouple from the microwave cavity
and thus preserve a long life-time. Our findings provide a promising approach
for developing long-lifetime, multimode quantum memories.Comment: 18 pages, 12 figure
Thermal Baths as Quantum Resources: More Friends than Foes?
In this article we argue that thermal reservoirs (baths) are potentially
useful resources in processes involving atoms interacting with quantized
electromagnetic fields and their applications to quantum technologies. One may
try to suppress the bath effects by means of dynamical control, but such
control does not always yield the desired results. We wish instead to take
advantage of bath effects, that do not obliterate "quantumness" in the
system-bath compound. To this end, three possible approaches have been pursued
by us: (i) Control of a quantum system faster than the correlation time of the
bath to which it couples: Such control allows us to reveal
quasi-reversible/coherent dynamical phenomena of quantum open systems, manifest
by the quantum Zeno or anti-Zeno effects (QZE or AZE, respectively). Dynamical
control methods based on the QZE are aimed not only at protecting the
quantumness of the system, but also diagnosing the bath spectra or transferring
quantum information via noisy media. By contrast, AZE-based control is useful
for fast cooling of thermalized quantum systems. (ii) Engineering the coupling
of quantum systems to selected bath modes: This approach, based on field -atom
coupling control in cavities, waveguides and photonic band structures, allows
to drastically enhance the strength and range of atom-atom coupling through the
mediation of the selected bath modes. More dramatically, it allows us to
achieve bath-induced entanglement that may appear paradoxical if one takes the
conventional view that coupling to baths destroys quantumness. (iii)
Engineering baths with appropriate non-flat spectra: This approach is a
prerequisite for the construction of the simplest and most efficient quantum
heat machines (engines and refrigerators). We may thus conclude that often
thermal baths are "more friends than foes" in quantum technologies.Comment: 27 pages, 17 figure
Control of Optical Dynamic Memory Capacity of an Atomic Bose-Einstein Condensate
Light storage in an atomic Bose-Einstein condensate is one of the most
practical usage of these coherent atom-optical systems. In order to make them
even more practical, it is necessary to enhance our ability to inject multiple
pulses into the condensate. In this paper, we report that dispersion of pulses
injected into the condensate can be compensated by optical nonlinearity. In
addition, we will present a brief review of our earlier results in which
enhancement of light storage capacity is accomplished by utilizing multi-mode
light propagation or choosing an optimal set of experimental parameters.Comment: 4 figures, 11 page
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