43,757 research outputs found
Gain without inversion in quantum systems with broken parities
For a quantum system with broken parity symmetry, selection rules can not
hold and cyclic transition structures are generated. With these
loop-transitions we discuss how to achieve inversionless gain of the probe
field by properly setting the control and auxiliary fields. Possible
implementations of our generic proposal with specific physical objects with
broken parities, e.g., superconducting circuits and chiral molecules, are also
discussed.Comment: 12 pages, 4 figure
Tunable one-dimensional microwave emissions from cyclic-transition three-level atoms
By strongly driving a cyclic-transition three-level artificial atom,
demonstrated by such as a flux-based superconducting circuit, we show that
coherent microwave signals can be excited along a coupled one-dimensional
transmission line. Typically, the intensity of the generated microwave is
tunable via properly adjusting the Rabi frequencies of the applied
strong-driving fields or introducing a probe field with the same frequency. In
practice, the system proposed here could work as an on-chip quantum device with
controllable atom-photon interaction to implement a total-reflecting mirror or
switch for the propagating probe field.Comment: 4 pages, 5 figure
Quantum state engineering with flux-biased Josephson phase qubits by Stark-chirped rapid adiabatic passages
In this paper, the scheme of quantum computing based on Stark chirped rapid
adiabatic passage (SCRAP) technique [L. F. Wei et al., Phys. Rev. Lett. 100,
113601 (2008)] is extensively applied to implement the quantum-state
manipulations in the flux-biased Josephson phase qubits. The broken-parity
symmetries of bound states in flux-biased Josephson junctions are utilized to
conveniently generate the desirable Stark-shifts. Then, assisted by various
transition pulses universal quantum logic gates as well as arbitrary
quantum-state preparations could be implemented. Compared with the usual
PI-pulses operations widely used in the experiments, the adiabatic population
passage proposed here is insensitive the details of the applied pulses and thus
the desirable population transfers could be satisfyingly implemented. The
experimental feasibility of the proposal is also discussed.Comment: 9 pages, 4 figure
Realizing quantum controlled phase-flip gate through quantum dot in silicon slow-light photonic crystal waveguide
We propose a scheme to realize controlled phase gate between two single
photons through a single quantum dot in slow-light silicon photonic crystal
waveguide. Enhanced Purcell factor and beta factor lead to high gate fidelity
over broadband frequencies compared to cavity-assisted system. The excellent
physical integration of this silicon photonic crystal waveguide system provides
tremendous potential for large-scale quantum information processing.Comment: 9 pages, 3 figure
Vacuum induced Berry phases in single-mode Jaynes-Cummings models
Motivated by the work [Phys. Rev. Lett. 89, 220404 (2002)] for detecting the
vacuum-induced Berry phases with two-mode Jaynes-Cummings models (JCMs), we
show here that, for a parameter-dependent single-mode JCM, certain atom-field
states also acquire the photon-number-dependent Berry phases after the
parameter slowly changed and eventually returned to its initial value. This
geometric effect related to the field quantization still exists, even the filed
is kept in its vacuum state. Specifically, a feasible Ramsey interference
experiment with cavity quantum electrodynamics (QED) system is designed to
detect the vacuum-induced Berry phase.Comment: 10 pages, 4 figures
Novel magnetic orderings in the kagome Kondo-lattice model
We consider the Kondo-lattice model on the kagome lattice and study its
weak-coupling instabilities at band filling fractions for which the Fermi
surface has singularities. These singularites include Dirac points, quadratic
Fermi points in contact with a flat band, and Van Hove saddle points. By
combining a controlled analytical approach with large-scale numerical
simulations, we demonstrate that the weak-coupling instabilities of the
Kondo-lattice model lead to exotic magnetic orderings. In particular, some of
these magnetic orderings produce a spontaneous quantum anomalous Hall state.Comment: 15 pages, 11 figure
Vortex Nucleation Induced Phonon Radiation from a Moving Electron Bubble in Superfluid 4He
We construct an efficient zero-temperature semi-local density functional to
dynamically simulate an electron bubble passing through superfluid 4He under
various pressures and electric fields up to nanosecond timescale. Our simulated
drift velocity can be quantitatively compared to experiments particularly when
pressure approaches zero. We find that the high-speed bubble experiences
remarkable expansion and deformation before vortex nucleation occurs.
Accompanied by vortex-ring shedding, drastic surface vibration is generated
leading to intense phonon radiation into the liquid. The amount of energy
dissipated by these phonons is found to be greater than the amount carried away
solely by the vortex rings. These results may enrich our understanding about
the vortex nucleation induced energy dissipation in this fascinating system.Comment: 7 pages, 5 figure
Generation of nonclassical photon states using a superconducting qubit in a microcavity
Based on the interaction between the radiation field and a superconductor, we
propose a way to engineer quantum states using a SQUID charge qubit inside a
microcavity. This device can act as a deterministic single photon source as
well as generate any Fock states and an arbitrary superposition of Fock states
for the cavity field. The controllable interaction between the cavity field and
the qubit can be realized by the tunable gate voltage and classical magnetic
field applied to the SQUID.Comment: 4 page
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