3,877 research outputs found
Enhanced energy relaxation process of quantum memory coupled with a superconducting qubit
For quantum information processing, each physical system has different
advantage for the implementation and so hybrid systems to benefit from several
systems would be able to provide a promising approach. One of the common hybrid
approach is to combine a superconducting qubit as a controllable qubit and the
other quantum system with a long coherence time as a memory qubit. The
superconducting qubit allows us to have an excellent controllability of the
quantum states and the memory qubit is capable of storing the information for a
long time. By tuning the energy splitting between the superconducting qubit and
the memory qubit, it is believed that one can realize a selective coupling
between them. However, we have shown that this approach has a fundamental
drawback concerning energy leakage from the memory qubit. The detuned
superconducting qubit is usually affected by severe decoherence, and this
causes an incoherent energy relaxation from the memory qubit to the
superconducting qubit via the imperfect decoupling. We have also found that
this energy transport can be interpreted as an appearance of anti quantum Zeno
effect induced by the fluctuation in the superconducting qubit. We also discuss
a possible solution to avoid such energy relaxation process, which is feasible
with existing technology
Quantum Zeno effect with a superconducting qubit
Detailed schemes are investigated for experimental verification of Quantum
Zeno effect with a superconducting qubit. A superconducting qubit is affected
by a dephasing noise whose spectrum is 1/f, and so the decay process of a
superconducting qubit shows a naturally non-exponential behavior due to an
infinite correlation time of 1/f noise. Since projective measurements can
easily influence the decay dynamics having such non-exponential feature, a
superconducting qubit is a promising system to observe Quantum Zeno effect. We
have studied how a sequence of projective measurements can change the dephasing
process and also we have suggested experimental ways to observe Quantum Zeno
effect with a superconducting qubit. It would be possible to demonstrate our
prediction in the current technology
Holographic QCD Integrated back to Hidden Local Symmetry
We develop a previously proposed gauge-invariant method to integrate out
infinite tower of Kaluza-Klein (KK) modes of vector and axialvector mesons in a
class of models of holographic QCD (HQCD). The HQCD is reduced by our method to
the chiral perturbation theory with the hidden local symmetry (HLS) having only
the lowest KK mode identified as the HLS gauge boson. We take the
Sakai-Sugimoto model as a concrete HQCD, and completely determine the terms as well as the terms from the DBI part and the
anomaly-related (intrinsic parity odd) gauge-invariant terms from the CS part.
Effects of higher KK modes are fully included in these terms. To demonstrate
power of our method, we compute momentum-dependences of several form factors
such as the pion electromagnetic form factors, the - and
- transition form factors compared with experiment, which was
not achieved before due to complication to handle infinite sums. We also study
other anomaly-related quantities like --- and
--- vertex functions.Comment: 4 eps figures, 37 pages, latex, typos fixed; some discussions and
references added; fig.4 replace
Quantum metrology beyond the classical limit under the effect of dephasing
Quantum sensors have the potential to outperform their classical
counterparts. For classical sensing, the uncertainty of the estimation of the
target fields scales inversely with the square root of the measurement time T.
On the other hand, by using quantum resources, we can reduce this scaling of
the uncertainty with time to 1/T. However, as quantum states are susceptible to
dephasing, it has not been clear whether we can achieve sensitivities with a
scaling of 1/T for a measurement time longer than the coherence time. Here, we
propose a scheme that estimates the amplitude of globally applied fields with
the uncertainty of 1/T for an arbitrary time scale under the effect of
dephasing. We use one-way quantum computing based teleportation between qubits
to prevent any increase in the correlation between the quantum state and its
local environment from building up and have shown that such a teleportation
protocol can suppress the local dephasing while the information from the target
fields keeps growing. Our method has the potential to realize a quantum sensor
with a sensitivity far beyond that of any classical sensor
Pionic BEC--BCS crossover at finite isospin chemical potential
We study the character change of the pionic condensation at finite isospin
chemical potential \mu_\mathrm{I} by adopting the linear sigma model as a
non-local interaction between quarks. At low |\mu_\mathrm{I}| the condensation
is purely bosonic, then the Cooper pairing around the Fermi surface grows
gradually as |\mu_\mathrm{I}| increases. This q-\bar q pairing is weakly
coupled in comparison with the case of the q-q pairing that leads to color
superconductivity.Comment: 17 pages, 3 figures, typos in eq.(6) and refs.[37] and [41] are
corrected, published in Phys. Rev.
Does the three site Higgsless model survive the electroweak precision tests at loop?
We complete the list of one loop renormalization group equations and matching
conditions relevant for the computation of the electroweak precision parameters
and in the three site Higgsless model. We obtain one-loop formulas for
and expressed in terms of physical observables such as the KK gauge
boson mass , the KK fermion mass , and the KK gauge boson ()
couplings with light quarks and leptons . It is shown that these
physical observables, , and are severely constrained by
the electroweak precision data. Unlike the tree level analysis on the ideally
delocalized fermion, we find that perfect fermiophobity of is ruled out by
the precision data. We also study the cutoff dependence of our analysis.
Although the model is non-renormalizable, the dependence on the cutoff
parameter is shown to be non-significant.Comment: 13pages, 5figures, minor corrections made, references adde
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