84 research outputs found
Constraining the generalized uncertainty principle with cold atoms
Various theories of quantum gravity predict the existence of a minimum length
scale, which implies the Planck-scale modifications of the Heisenberg
uncertainty principle to a so-called generalized uncertainty principle (GUP).
Previous studies of the GUP focused on its implications for high-energy
physics, cosmology, and astrophysics. Here, the application of the GUP to
low-energy quantum systems, and particularly cold atoms, is studied. Results
from the Rb atom recoil experiment are used to set upper bounds on
parameters in three different GUP proposals. A -level bound on the
Ali-Das-Vagenas proposal is found, which is the second best bound so far. A
-level bound on Maggiore's proposal is obtained, which turns out to be
the best available bound on it
Preparing remotely two instances of quantum state
In this short note, we propose a scheme, in which two instances of an
equatorial state (or a polar state) can be remotely prepared in one-shot
operation to different receivers with prior entanglement and 1 bit of
broadcasting. The trade-off curve between the amount of entanglement and the
achievable fidelity is derived.Comment: 7 pages, 1 figur
Density expectation value of two independent interacting Bose-Einstein condensates
After removing the double-well potential trapping two initially independent
Bose condensates, the density expectation value is calculated when both the
exchange symmetry of identical bosons and interatomic interaction are
considered. After the overlapping, it is shown that there is a nonzero
interference term in the density expectation value. This nonzero interference
term physically arises from the exchange symmetry of identical bosons and
interatomic interaction which make two initially independent condensates become
coherent after the overlapping. It is found that the calculated density
expectation value with this model agrees with the interference pattern observed
in the experiment by Andrews et al (Science 275, 637 (1997)).Comment: 4 pages, 2 figures. We consider in the present work a quite
challenging problem. Any comments are welcom
Constraining the generalized uncertainty principle with the atomic weak-equivalence-principle test
Various models of quantum gravity imply the Planck-scale modifications of
Heisenberg's uncertainty principle into a so-called generalized uncertainty
principle (GUP). The GUP effects on high-energy physics, cosmology, and
astrophysics have been extensively studied. Here, we focus on the
weak-equivalence-principle (WEP) violation induced by the GUP. Results from the
WEP test with the Rb-Rb dual-species atom interferometer are used
to set upper bounds on parameters in two GUP proposals. A -level bound
on the Kempf-Mangano-Mann proposal, and a -level bound on Maggiore's
proposal, which are consistent with bounds from other experiments, are
obtained. All these bounds have huge room for improvement in the future.Comment: 7 pages, 1 figur
Dimers of ultracold two-component Fermi gases on magnetic-field Feshbach resonance
At the location of a magnetic-field Feshbach resonance, a mixture gas of
fermionic atoms and dimers of fermionic atom pairs is investigated in the
unitarity limit where the absolute value of the scattering length is much
larger than the mean distance between atoms. The dynamic equilibrium of the
mixture gases is characterized by the minimum of the Gibbs free energy. For the
fermionic atoms and dimers with divergent scattering length, it is found that
the fraction of the dimers based on a very simple theory agrees with the high
fraction of zero-momentum molecules observed in a recent experiment (M. W.
Zwierlein et al, Phys. Rev. Lett. 92, 120403 (2004)). The dimeric gas can be
also used to interpret the frequency of the radial breathing mode observed in
the experiment by J. Kinast et al (Phys. Rev. Lett. 92, 150402 (2004)).Comment: RevTex, 4 page
Josephson effect and quantum merging of two Bose superfluids
We consider the Josephson effect when two independent Bose superfluids are
weakly connected. In the presence of interparticle interaction and based on the
calculations of the one-particle density matrix of the whole system, we find
that the one-particle density matrix can be factorized which satisfies the
general criterion of Bose superfluid proposed by Penrose and Onsager. By
introducing an effective order parameter for the whole system, our researches
show that there is Josephson effect for two independent Bose superfluids.Comment: 9 pages, 4 figures. two typos in Eqs. (19) and (22) are corrected in
this versio
Disentangling and broadcasting an entangled state simultaneously by asymmetric cloning
We construct a quantum machine which, by using asymmetric cloner, deals with
disentangling and broadcasting entanglement in a single unitary evolution. The
attainable maximum value of the scaling parameter for disentangling is
identical to that obtained in previous works. The fidelity of the cloning state
with respect to the input entangled state is state-dependent.Comment: 5 page
Correlation, entropy, and information transfer in black hole radiation
Since the discovery of Hawking radiation, its consistency with quantum theory
has been widely questioned. In the widely described picture, irrespective of
what initial state a black hole starts with before collapsing, it eventually
evolves into a thermal state of Hawking radiations after the black hole is
exhausted. This scenario violates the principle of unitarity as required for
quantum mechanics and leads to the acclaimed "information loss paradox". This
paradox has become an obstacle or a reversed touchstone for any possible theory
to unify the gravity and quantum mechanics. Based on the results from Hawking
radiation as tunneling, we recently show that Hawking radiations can carry off
all information about the collapsed matter in a black hole. After discovering
the existence of information-carrying correlation, we show in great detail that
entropy is conserved for Hawking radiation based on standard probability theory
and statistics. We claim that information previously considered lost remains
hidden inside Hawking radiation. More specifically, it is encoded into
correlations between Hawking radiations. Our study thus establishes harmony
between Harking radiation and the unitarity of quantum mechanics, which
establishes the basis for a significant milestone towards resolving the
long-standing information loss paradox. The paper provides a brief review of
the exciting development on Hawking raidation. In addition to summarize our own
work on this subject, we compare and address other related studies
Two-object remote quantum control
We consider the two-object remote quantum control for a special case in which
all the object qubits are in a telecloning state. We propose a scheme which
achieves the two-object remote quantum control by using two particular
four-particle entangled states.Comment: 4 pages, 1 figur
A Theorem Prover for Quantum Hoare Logic and Its Applications
Quantum Hoare Logic (QHL) was introduced in Ying's work to specify and reason
about quantum programs. In this paper, we implement a theorem prover for QHL
based on Isabelle/HOL. By applying the theorem prover, verifying a quantum
program against a specification is transformed equivalently into an order
relation between matrices. Due to the limitation of Isabelle/HOL, the
calculation of the order relation is solved by calling an outside oracle
written in Python. To the best of our knowledge, this is the first theorem
prover for quantum programs. To demonstrate its power, the correctness of two
well-known quantum algorithms, i.e., Grover Quantum Search and Quantum Phase
Estimation (the key step in Shor's quantum algorithm of factoring in polynomial
time) are proved using the theorem prover. These are the first mechanized
proofs for both of them
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