We propose a large-scale quantum computer architecture by stabilizing a
single large linear ion chain in a very simple trap geometry. By confining ions
in an anharmonic linear trap with nearly uniform spacing between ions, we show
that high-fidelity quantum gates can be realized in large linear ion crystals
under the Doppler temperature based on coupling to a near-continuum of
transverse motional modes with simple shaped laser pulses.
We propose and experimentally investigate a fibre-based quantum key
distribution system, which employs polarization qubits encoded into faint laser
pulses. As a novel feature, it allows sending of classical framing information
via sequences of strong laser pulses that precede the quantum data. This allows
synchronization, sender and receiver identification, and compensation of
time-varying birefringence in the communication channel. In addition, this
method also provides a platform to communicate implementation specific
information such as encoding and protocol in view of future optical quantum
networks. Furthermore, we report on our current effort to develop high-rate
error correction.
Within the framework of macroscopic quantum electrodynamics in linear, causal
media, we study the van der Waals potentials of ground-state atoms in planar
magnetodielectric host media. Our investigation extends earlier ones in two
aspects: It allows for the atom to be embedded in a medium, thus covers many
more realistic systems; and it takes account of the local-field correction.
Two- and three-layer configurations are treated in detail both analytically and
numerically. It is shown that an interplay of electric and magnetic properties
in neighbouring media may give rise to potential wells or walls. Local-field
corrections as high as 80% are found. By calculating the full potential
including the translationally invariant and variant parts, we propose a way to
estimate the (finite) value of the dispersion potential at the surface between
two media. Connection with earlier work intended for biological applications is
established.
Title:
Any l-state improved quasi-exact analytical solutions of the spatially
dependent mass Klein-Gordon equation for the scalar and vector Hulthen
potentials
Authors:
Sameer M. Ikhdair,
Ramazan Sever
We present a new approximation scheme for the centrifugal term to obtain a
quasi-exact analytical bound state solutions within the framework of the
position-dependent effective mass radial Klein-Gordon equation with the scalar
and vector Hulth\'{e}n potentials in any arbitrary $D$ dimension and orbital
angular momentum quantum numbers $l.$ The Nikiforov-Uvarov (NU) method is used
in the calculations. The relativistic real energy levels and corresponding
eigenfunctions for the bound states with different screening parameters have
been given in a closed form. It is found that the solutions in the case of
constant mass and in the case of s-wave ($l=0$) are identical with the ones
obtained in literature.
We discuss the feasibility of negative refraction with reduced absorption in
coherently driven atomic media. Coherent coupling of an electric and a magnetic
dipole transition by laser fields induces magneto-electric cross-coupling and
negative refraction at dipole densities which are considerably smaller than
necessary to achieve a negative permeability. At the same time the absorption
gets minimized due to destructive quantum interference and the ratio of
negative refraction index to absorption becomes orders of magnitude larger than
in systems without coherent cross-coupling. The proposed scheme allows for a
fine-tuning of the refractive index. We derive a generalized expression for the
impedance of a medium with magneto-electric cross coupling and show that
impedance matching to vacuum can easily be achieved. Finally we discuss the
tensorial properties of the medium response and derive expressions for the
dependence of the refractive index on the propagation direction.
Evolution of a many particles on a one dimensional lattice subjected to
quantum walk can cause entanglement (spatial entanglement) in the lattice
position. This entanglement seems to depend on quantum coin parameters, number
of particles present in the lattice and the number of steps of quantum walk the
system is subjected to. The evolution of spatial entanglement has been studied
with respect to all the parameters mentioned above on many particle in one
dimensional open and closed chains.
Title:
Three-Hilbert-Space Formulation of Quantum Mechanics
Authors:
Miloslav Znojil
In paper [Znojil M., Phys. Rev. D 78 (2008), 085003, 5 pages,
arXiv:0809.2874] the two-Hilbert-space (2HS, a.k.a. cryptohermitian)
formulation of Quantum Mechanics has been revisited. In the present
continuation of this study (with the spaces in question denoted as ${\cal
H}^{\rm (auxiliary)}$ and ${\cal H}^{\rm (standard)}$) we spot a weak point of
the 2HS formalism which lies in the double role played by ${\cal H}^{\rm
(auxiliary)}$. As long as this confluence of roles may (and did!) lead to
confusion in the literature, we propose an amended, three-Hilbert-space (3HS)
reformulation of the same theory. As a byproduct of our analysis of the
formalism we offer an amendment of the Dirac's bra-ket notation and we also
show how its use clarifies the concept of covariance in time-dependent cases.
Via an elementary example we finally explain why in certain quantum systems the
generator $H_{\rm (gen)}$ of the time-evolution of the wave functions may
differ from their Hamiltonian $H$.
Title:
An amplitude-phase (Ermakov-Lewis) approach for the Jackiw-Pi model of
bilayer graphene
Authors:
K. V. Khmelnytskaya,
H. C. Rosu
In the context of bilayer graphene we use the simple gauge model of Jackiw
and Pi to construct its numerical solutions in powers of the bias potential V
according to a general scheme due to Kravchenko. Next, using this numerical
solutions, we develop the Ermakov-Lewis approach for the same model. This leads
us to numerical calculations of the Lewis-Riesenfeld phases that could be of
forthcoming experimental interest for bilayer graphene. We also present a
generalization of the Ioffe-Korsch nonlinear Darboux transformation
In realizations of quantum computing, a two-level system (qubit) is often
singled out of the many levels of an anharmonic oscillator. In these cases,
simple qubit control fails on short time scales because of coupling to leakage
levels. We provide an easy to implement analytic formula that inhibits this
leakage from any single-control analog or pixelated pulse. It is based on
adding a second control that is proportional the time-derivative of the first.
For realistic parameters of superconducting qubits, this strategy reduces the
error by an order of magnitude relative to the state of the art, all based on
smooth and feasible pulse shapes. These results show that even weak
anharmonicity is sufficient and in general not a limiting factor for
implementing quantum gates.
0812.4622preskill : It seems to me that there may be another reason why (logarithmic) confinement of defects due to Coulombic interactions should not be regarde...
I agree with Matt's criticism of this paper. In fact if we allow Hamiltonians in 2D with norms of terms scaling with system s...
0807.3369Benni : At 13.12.2008 I got the referee report (after four months or so). The referees said, that the main conclusions of my paper would be correct....
0812.4622matt.hastings : This is a problem that many people have worked on, namely how to construct a model with topological order at non-zero temperature in 2 or 3 ...
0812.4614QuantumMoxie : Not sure what to make of this. On the one hand, it's a potentially interesting problem. On the other hand, "dangerous?"
0812.3058QuantumMoxie : OK foundations people, this should spark interesting debate (I would think) since Nieuwenhuizen generally isn't a total kook.
0812.0171pak : I'm not convinced that the NPV (LH) condition discussed is "inapplicable for active materials", as claimed here. As far as I can tell, the c...
0811.4542dabacon : What Scott said: http://scottaaronson.com/blog/?p=369
0811.3171jimh : This could very well be a "killer app" for a quantum computer. I remember at a physics colloquium in spring 1998 someone in the audience as...