593 research outputs found
Mesoscopic Rydberg Gate based on Electromagnetically Induced Transparency
We demonstrate theoretically a parallelized C-NOT gate which allows to
entangle a mesoscopic ensemble of atoms with a single control atom in a single
step, with high fidelity and on a microsecond timescale. Our scheme relies on
the strong and long-ranged interaction between Rydberg atoms triggering
Electromagnetically Induced Transparency (EIT). By this we can robustly
implement a conditional transfer of all ensemble atoms among two logical
states, depending on the state of the control atom. We outline a many body
interferometer which allows a comparison of two many-body quantum states by
performing a measurement of the control atom.Comment: published versio
Radiation damage to nucleoprotein complexes in macromolecular crystallography
Significant progress has been made in macromolecular crystallography over recent years in both the understanding and mitigation of X-ray induced radiation damage when collecting diffraction data from crystalline proteins. In contrast, despite the large field that is productively engaged in the study of radiation chemistry of nucleic acids, particularly of DNA, there are currently very few X-ray crystallographic studies on radiation damage mechanisms in nucleic acids. Quantitative comparison of damage to protein and DNA crystals separately is challenging, but many of the issues are circumvented by studying pre-formed biological nucleoprotein complexes where direct comparison of each component can be made under the same controlled conditions. Here a model protein-DNA complex C.Esp1396I is employed to investigate specific damage mechanisms for protein and DNA in a biologically relevant complex over a large dose range (2.07-44.63 MGy). In order to allow a quantitative analysis of radiation damage sites from a complex series of macromolecular diffraction data, a computational method has been developed that is generally applicable to the field. Typical specific damage was observed for both the protein on particular amino acids and for the DNA on, for example, the cleavage of base-sugar N1-C and sugar-phosphate C-O bonds. Strikingly the DNA component was determined to be far more resistant to specific damage than the protein for the investigated dose range. At low doses the protein was observed to be susceptible to radiation damage while the DNA was far more resistant, damage only being observed at significantly higher doses
Universal Quantum Cloning in Cavity QED
We propose an implementation of an universal quantum cloning machine [UQCM,
Hillery and Buzek, Phys. Rev. A {\bf 56}, 3446 (1997)] in a Cavity Quantum
Electrodynamics (CQED) experiment. This UQCM acts on the electronic states of
atoms that interact with the electromagnetic field of a high cavity. We
discuss here the specific case of the cloning process using either a
one- or a two-cavity configuration
Jaynes-Cummings Models with trapped surface-state electrons in THz cavities
An electron floating on the liquid Helium is proposed to be trapped (by a
micro-electrode set below the liquid Helium) in a high finesse cavity. Two
lowest levels of the vertical motion of the electron acts as a two-level
"atom", which could resonantly interact with the THz cavity. In the Lamb-Dicke
regime, wherein the electron's in-plane activity region is much smaller than
the wavelength of the cavity mode, the famous Jaynes-Cummings model (JCM) could
be realized. By applying an additional external classical laser beam to the
electron, a driven JCM could also be implemented. With such a driven JCM
certain quantum states, e.g., coherent states and the Schrodinger cat states,
of the THz cavity field could be prepared by one-step evolution. The numerical
results show that, for the typical parameters of the cavity and electron on
liquid Helium, a strong coupling between the artificial atom and the THz cavity
could be obtained.Comment: 11 pages, 1 figure
Single Atom and Two Atom Ramsey Interferometry with Quantized Fields
Implications of field quantization on Ramsey interferometry are discussed and
general conditions for the occurrence of interference are obtained.
Interferences do not occur if the fields in two Ramsey zones have precise
number of photons. However in this case we show how two atom (like two photon)
interferometry can be used to discern a variety of interference effects as the
two independent Ramsey zones get entangled by the passage of first atom.
Generation of various entangled states like |0,2>+|2,0> are discussed and in
far off resonance case generation of entangled state of two coherent states is
discussed.Comment: 20 pages, 5 figures, revised version. submitted to Phys. Rev.
Quantum Search with Two-atom Collisions in Cavity QED
We propose a scheme to implement two-qubit Grover's quantum search algorithm
using Cavity Quantum Electrodynamics. Circular Rydberg atoms are used as
quantum bits (qubits). They interact with the electromagnetic field of a
non-resonant cavity . The quantum gate dynamics is provided by a
cavity-assisted collision, robust against decoherence processes. We present the
detailed procedure and analyze the experimental feasibility.Comment: 4 pages, 2 figure
On the Lieb-Liniger model in the infinite coupling constant limit
We consider the one-dimensional Lieb-Liniger model (bosons interacting via
2-body delta potentials) in the infinite coupling constant limit (the so-called
Tonks-Girardeau model). This model might be relevant as a description of atomic
Bose gases confined in a one-dimensional geometry. It is known to have a
fermionic spectrum since the N-body wavefunctions have to vanish at coinciding
points, and therefore be symmetrizations of fermionic Slater wavefunctions. We
argue that in the infinite coupling constant limit the model is
indistinguishable from free fermions, i.e., all physically accessible
observables are the same as those of free fermions. Therefore, Bose-Einstein
condensate experiments at finite energy that preserve the one-dimensional
geometry cannot test any bosonic characteristic of such a model
A proposal for the implementation of quantum gates with photonic-crystal coupled cavity waveguides
Quantum computers require technologies that offer both sufficient control
over coherent quantum phenomena and minimal spurious interactions with the
environment. We show, that photons confined to photonic crystals, and in
particular to highly efficient waveguides formed from linear chains of defects
doped with atoms can generate strong non-linear interactions which allow to
implement both single and two qubit quantum gates. The simplicity of the gate
switching mechanism, the experimental feasibility of fabricating two
dimensional photonic crystal structures and integrability of this device with
optoelectronics offers new interesting possibilities for optical quantum
information processing networks.Comment: 4 pages, 3 figure
Universality of Decoherence
We consider environment induced decoherence of quantum superpositions to
mixtures in the limit in which that process is much faster than any competing
one generated by the Hamiltonian of the isolated system. While
the golden rule then does not apply we can discard . By allowing
for simultaneous couplings to different reservoirs, we reveal decoherence as a
universal short-time phenomenon independent of the character of the system as
well as the bath and of the basis the superimposed states are taken from. We
discuss consequences for the classical behavior of the macroworld and quantum
measurement: For the decoherence of superpositions of macroscopically distinct
states the system Hamiltonian is always negligible.Comment: 4 revtex pages, no figure
Deuterons and space-momentum correlations in high energy nuclear collisions
Using a microscopic transport model together with a coalescence after-burner, we study the formation of deuterons in Au + Au central collisions at s = 200 AGeV . It is found that the deuteron transverse momentum distributions are strongly a ected by the nucleon space-momentum correlations, at the moment of freeze-out, which are mostly determined by the number of rescatterings. This feature is useful for studying collision dynamics at ultrarelativistic energies
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