12,677 research outputs found
Local manipulation of quantum magnetism in 1D ultracold Fermi gases across narrow resonances
Effective range is a quantity to characterize the energy dependence in
two-body scattering strength, and is widely used in cold atomic systems
especially across narrow resonances. Here we show that the effective range can
significantly modify the magnetic property of one-dimensional (1D) spin-
fermions in the strongly repulsive regime. In particular, the effective range
breaks the large spin degeneracy in the hard-core limit, and induces a
Heisenberg exchange term in the spin chain that is much more sensitive to the
local density than that induced by the bare coupling. With an external harmonic
trap, this leads to a very rich magnetic pattern where the anti-ferromagnetic
(AFM) and ferromagnetic (FM) correlations can coexist and distribute in highly
tunable regions across the trap. Finally, we propose to detect the
range-induced magnetic order in the tunneling experiment. Our results can be
directly tested in 1D Fermi gases across narrow resonance, and suggest a
convenient route towards the local manipulation of quantum magnetism in cold
atoms.Comment: 5 pages, 6 figure
High order exceptional points in ultracold Bose gases
We show that arbitrarily high-order exceptional points (EPs) can be achieved
in a repulsively interacting two-species Bose gas in one dimension. By exactly
solving the non-Hermitian two-boson problem, we demonstrate the existence of
third-order EPs when the system is driven across the parity-time symmetry
breaking transition. We further address the fourth-order EPs with three bosons
and generalize the results to -body system, where the EP order can be as
high as . Physically, such high order originates from the intrinsic
ferromagnetic correlation in spinor bosons, which renders the entire system
collectively behave as a single huge spin. Moreover, we show how to create
ultra-sensitive spectral response around EPs via an interaction anisotropy in
different spin channels. Our work puts forward the possibility of atomic
sensors made from highly controllable ultracold gases.Comment: 6 pages, 4 figure
Non-Markovian entanglement dynamics between two coupled qubits in the same environment
We analyze the dynamics of the entanglement in two independent non-Markovian
channels. In particular, we focus on the entanglement dynamics as a function of
the initial states and the channel parameters like the temperature and the
ratio between the characteristic frequency of the quantum system
of interest, and the cut-off frequency of Ohmic reservoir. We give a
stationary analysis of the concurrence and find that the dynamic of
non-markovian entanglement concurrence at temperature
is different from the case. We find that "entanglement sudden
death" (ESD) depends on the initial state when , otherwise the
concurrence always disappear at finite time when , which means that ESD
must happen. The main result of this paper is that the non-Markovian
entanglement dynamic is fundamentally different from the Markovian one. In the
Markovian channel, entanglement decays exponentially and vanishes only
asymptotically, but in the non-Markovian channel the concurrence
oscillates, especially in the high temperature case.
Then an open-loop controller adjusted by the temperature is proposed to control
the entanglement and prolong the ESD time.Comment: 14 pages, 7 figure
Optimal control of population transfer in Markovian open quantum systems
There has long been interest to control the transfer of population between
specified quantum states. Recent work has optimized the control law for closed
system population transfer by using a gradient ascent pulse engineer- ing
algorithm [1]. Here, a spin-boson model consisting of two-level atoms which
interact with the dissipative environment, is investigated. With opti- mal
control, the quantum system can invert the populations of the quantum logic
states. The temperature plays an important role in controlling popula- tion
transfer. At low temperatures the control has active performance, while at high
temperatures it has less erect. We also analyze the decoherence be- havior of
open quantum systems with optimal population transfer control, and we find that
these controls can prolong the coherence time. We hope that active optimal
control can help quantum solid-state-based engineering.Comment: 19 pages, 10 figure
Optimal control of non-Markovian open quantum systems via feedback
The problem of optimal control of non-Markovian open quantum system via weak
measurement is presented. Based on the non-Markovian master equation, we
evaluate exactly the non-Markovian effect on the dynamics of the system of
interest interacting with a dissipative reservoir. We find that the
non-Markovian reservoir has dual effects on the system: dissipation and
backaction. The dissipation exhausts the coherence of the quantum system,
whereas the backaction revives it. Moreover, we design the control Hamiltonian
with the control laws attained by the stochastic optimal control and the
corresponding optimal principle. At last, we considered the exact decoherence
dynamics of a qubit in a dissipative reservoir composed of harmonic
oscillators, and demonstrated the effectiveness of our optimal control
strategy. Simulation results showed that the coherence will completely lost in
the absence of control neither in non-Markovian nor Markovian system. However,
the optimal feedback control steers it to a stationary stochastic process which
fluctuates around the target. In this case the decoherence can be controlled
effectively, which indicates that the engineered artificial reservoirs with
optimal feedback control may be designed to protect the quantum coherence in
quantum information and quantum computation.Comment: 15 pages, 2 figure
Interacting non-Hermitian ultracold atoms in a harmonic trap: Two-body exact solution and high-order exceptional point
We study interacting ultracold atoms in a three-dimensional (3D) harmonic
trap with spin-selective dissipations, which can be effectively described by
non-Hermitian parity-time () symmetric Hamiltonians. By solving
the non-Hermitian two-body problem of spin-1/2 (spin-1) bosons in a 3D harmonic
trap exactly, we find that the system can exhibit third-order (fifth-order)
exceptional point (EP) with ultra-sensitive cube-root (fifth-root) spectral
response due to interaction anisotropies in spin channels. We also present the
general principle for the creation of high-order EPs and their spectral
sensitivities with arbitrary particle number and arbitrary spin .
Generally, with spin-independent interactions, the EP order of bosons can be as
high as , and the spectral response around EP can be as sensitive as
under a -body interaction anisotropy. Moreover,
we propose to detect the ultra-sensitive spectral response through the
probability dynamics of certain state. These results suggest a convenient route
towards more powerful sensor devices in spinor cold atomic systems.Comment: 13 pages, 7 figures
Electrical control of magnetism in oxides
This review article aims at illustrating the recent progresses in the
electrical control of magnetism in oxides with profound physics and enormous
potential applications. In the first part, we provide a comprehensive summary
of the electrical control of magnetism in the classic multiferroic
heterostructures and clarify their various mechanisms lying behind. The second
part focuses on the novel route of electric double layer gating for driving a
significantly electronic phase transition in magnetic oxides by a small
voltage. The electric field applied on the ordinary dielectric oxide in the
third part is used to control the magnetic phenomenon originated from the
charge transfer and orbital reconstruction at the interface between dissimilar
correlated oxides. At last, we analyze the challenges in electrical control of
magnetism in oxides, both on mechanism and practical application, which would
inspire more in-depth researches and advance the development in this field.Comment: 41 pages, 13 figures, to be appeared in Chinese Physics B. arXiv
admin note: text overlap with arXiv:1307.5557 by other author
Topological Fulde-Ferrell states in alkaline-earth-metal-like atoms near an orbital Feshbach resonance
We study the effects of synthetic spin-orbit coupling on the pairing physics
in quasi-one-dimensional ultracold Fermi gases of alkaline-earth-metal-like
atoms near an orbital Feshbach resonance (OFR). The interplay between
spin-orbit coupling and pairing interactions near the OFR leads to an
interesting topological Fulde-Ferrell state, where the nontrivial topology of
the state is solely encoded in the closed channel with a topologically trivial
Fulde-Ferrell pairing in the open channel. We confirm the topological property
of the system by characterizing the Zak phase and the edge states. The
topological Fulde-Ferrell state can be identified by the momentum-space density
distribution obtained from time-of-flight images.Comment: 6 pages, 5 figure
Twin-Load: Building a Scalable Memory System over the Non-Scalable Interface
Commodity memory interfaces have difficulty in scaling memory capacity to
meet the needs of modern multicore and big data systems. DRAM device density
and maximum device count are constrained by technology, package, and signal in-
tegrity issues that limit total memory capacity. Synchronous DRAM protocols
require data to be returned within a fixed latency, and thus memory extension
methods over commodity DDRx interfaces fail to support scalable topologies.
Current extension approaches either use slow PCIe interfaces, or require
expensive changes to the memory interface, which limits commercial
adoptability. Here we propose twin-load, a lightweight asynchronous memory
access mechanism over the synchronous DDRx interface. Twin-load uses two
special loads to accomplish one access request to extended memory, the first
serves as a prefetch command to the DRAM system, and the second asynchronously
gets the required data. Twin-load requires no hardware changes on the processor
side and only slight soft- ware modifications. We emulate this system on a
prototype to demonstrate the feasibility of our approach. Twin-load has
comparable performance to NUMA extended memory and outperforms a page-swapping
PCIe-based system by several orders of magnitude. Twin-load thus enables
instant capacity increases on commodity platforms, but more importantly, our
architecture opens opportunities for the design of novel, efficient, scalable,
cost-effective memory subsystems.Comment: submitted to PACT1
Revisit of cosmic ray antiprotons from dark matter annihilation with updated constraints on the background model from AMS-02 and collider data
We study the cosmic ray antiprotons with updated constraints on the
propagation, proton injection, and solar modulation parameters based on the
newest AMS-02 data near the Earth and Voyager data in the local interstellar
space, and on the cross section of antiproton production due to proton-proton
collisions based on new collider data. We use a Bayesian approach to properly
consider the uncertainties of the model predictions of both the background and
the dark matter (DM) annihilation components of antiprotons. We find that
including an extra component of antiprotons from the annihilation of DM
particles into a pair of quarks can improve the fit to the AMS-02 antiproton
data considerably. The favored mass of DM particles is about GeV,
and the annihilation cross section is just at the level of the thermal
production of DM ( cm~s).Comment: 15 pages, 5 figures and 1 table; JCAP accepted versio
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