15,106 research outputs found
The Third Law of Quantum Thermodynamics in the Presence of Anomalous Couplings
The quantum thermodynamic functions of a harmonic oscillator coupled to a
heat bath through velocity-dependent coupling are obtained analytically. It is
shown that both the free energy and the entropy decay fast with the temperature
in relation to that of the usual coupling from. This implies that the
velocity-dependent coupling helps to ensure the third law of thermodynamics.Comment: 4 pages, 3 figures, 22 conference
Theory of control of spin/photon interface for quantum networks
A cavity coupling a charged nanodot and a fiber can act as a quantum
interface, through which a stationary spin qubit and a flying photon qubit can
be inter-converted via cavity-assisted Raman process. This Raman process can be
controlled to generate or annihilate an arbitrarily shaped single-photon
wavepacket by pulse-shaping the controlling laser field. This quantum interface
forms the basis for many essential functions of a quantum network, including
sending, receiving, transferring, swapping, and entangling qubits at
distributed quantum nodes as well as a deterministic source and an efficient
detector of a single photon wavepacket with arbitrarily specified shape and
average photon number. Numerical study of noise effects on the operations shows
high fidelity.Comment: 4 pages, 2 figure
Incommensurate magnetic structure of CeRhIn5
The magnetic structure of the heavy fermion antiferromagnet CeRhIn5 is
determined using neutron diffraction. We find a magnetic wave vector
q_M=(1/2,1/2,0.297), which is temperature independent up to T_N=3.8K. A
staggered moment of 0.374(5) Bohr magneton at 1.4K, residing on the Ce ion,
spirals transversely along the c axis. The nearest neighbor moments on the
tetragonal basal plane are aligned antiferromagnetically.Comment: 4 pages, 4 figures There was an extra factor of 2 in Eq (2). This
affects the value of staggered moment. The correct staggered moment is
0.374(5) Bohr magneton at 1.4
Deduction of the quantum numbers of low-lying states of 6-nucleon systems based on symmetry
The inherent nodal structures of the wavefunctions of 6-nucleon systems have
been investigated. The existence of a group of six low-lying states dominated
by L=0 has been deduced. The spatial symmetries of these six states are found
to be mainly {4,2} and {2,2,2}.Comment: 8 pages, no figure
Improved Simulation of the Mass Charging for ASTROD I
The electrostatic charging of the test mass in ASTROD I (Astrodynamical Space
Test of Relativity using Optical Devices I) mission can affect the quality of
the science data as a result of spurious Coulomb and Lorentz forces. To
estimate the size of the resultant disturbances, credible predictions of
charging rates and the charging noise are required. Using the GEANT4 software
toolkit, we present a detailed Monte Carlo simulation of the ASTROD I test mass
charging due to exposure of the spacecraft to galactic cosmic-ray (GCR) protons
and alpha particles (3He, 4He) in the space environment. A positive charging
rate of 33.3 e+/s at solar minimum is obtained. This figure reduces by 50% at
solar maximum. Based on this charging rate and factoring in the contribution of
minor cosmic-ray components, we calculate the acceleration noise and stiffness
associated with charging. We conclude that the acceleration noise arising from
Coulomb and Lorentz effects are well below the ASTROD I acceleration noise
limit at 0.1 mHz both at solar minimum and maximum. The coherent Fourier
components due to charging are investigated, it needs to be studied carefully
in order to ensure that these do not compromise the quality of science data in
the ASTROD I mission.Comment: 20 pages, 14 figures, submitted to International Journal of Modern
Physics
Quantum control of electron--phonon scatterings in artificial atoms
The phonon-induced dephasing dynamics in optically excited semiconductor
quantum dots is studied within the frameworks of the independent Boson model
and optimal control. We show that appropriate tailoring of laser pulses allows
a complete control of the optical excitation despite the phonon dephasing, a
finding in marked contrast to other environment couplings.Comment: to appear in Phys. Rev. Let
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