Steady-state entanglement in a double-well Bose-Einstein condensate through coupling to a superconducting resonator

We consider a two-component Bose-Einstein condensate in a double-well potential, where the atoms are magnetically coupled to a single-mode of the microwave field inside a superconducting resonator. We find that the system has the different dark-state subspaces in the strong- and weak-tunneling regimes, respectively. In the limit of weak tunnel coupling, steady-state entanglement between the two spatially separated condensates can be generated by evolving to a mixture of dark states via the dissipation of the photon field. We show that the entanglement can be faithfully indicated by an entanglement witness. Long-lived entangled states are useful for quantum information processing with atom-chip devices.Comment: 9 pages, 7 figures, minor revisio

Coherent control of atomic spin currents in a double well

We propose an experimental feasible method for controlling the atomic currents of a two-component Bose-Einstein condensate in a double well by applying an external field to the atoms in one of the potential wells. We study the ground-state properties of the system and show that the directions of spin currents and net-particle tunneling can be manipulated by adiabatically varying the coupling strength between the atoms and the field. This system can be used for studying spin and tunneling phenomena across a wide range of interaction parameters. In addition, spin-squeezed states can be generated. It is useful for quantum information processing and quantum metrology.Comment: 6 pages, 7 figures, minor revisio

A unified approach to realize universal quantum gates in a coupled two-qubit system with fixed always-on coupling

We demonstrate that in a coupled two-qubit system any single-qubit gate can be decomposed into two conditional two-qubit gates and that any conditional two-qubit gate can be implemented by a manipulation analogous to that used for a controlled two-qubit gate. Based on this we present a unified approach to implement universal single-qubit and two-qubit gates in a coupled two-qubit system with fixed always-on coupling. This approach requires neither supplementary circuit or additional physical qubits to control the coupling nor extra hardware to adjust the energy level structure. The feasibility of this approach is demonstrated by numerical simulation of single-qubit gates and creation of two-qubit Bell states in rf-driven inductively coupled two SQUID flux qubits with realistic device parameters and constant always-on coupling.Comment: 4 pages, 3 figure

A VLSI design for a systolic Viterbi decoder

A systolic Viterbi decoder for convolutional codes is developed. This decoder uses the trace-back method to reduce the amount of data needed to be stored in registers. It is shown that this new algorithm requires a smaller chip size and achieves a faster decoding time than other existing methods

Hydrogen atoms in circularly polarized microwave fields: Near-integrability and ionization

This is the published version, also available here: http://dx.doi.org/10.1103/PhysRevA.52.1358.We have recently found that the hydrogen atom in a circularly polarized (CP) microwave field possesses an approximate dynamical symmetry and its bounded motion can be well described by a three-dimensional integrable (but nonseparable) Hamiltonian function with a velocity-dependent potential [Raković and Chu, Phys. Rev. A 50, 5077 (1994)]. This finding provides a theoretical foundation for the understanding of the origin of the regularity of Rydberg atom dynamics in CP fields. We describe here the phase space topology of the three-dimensional integrable system relevant to the microwave ionization of the hydrogen atoms in CP fields. Using the integrable system as an approximation to the real system and with the use of the two additional integrals of motion, we are able to trace the deformation of the tori up to the point of bifurcation (ionization). From this, we have determined the classical ionization-field threshold law fth≊1/cn40, where n0 is the principal quantum number of the initial state of the hydrogen atom and c is almost a constant (≊6 a.u.). These results are in good accord with the existing experimental observations

Approximate dynamical symmetry of hydrogen atoms in circularly polarized microwave fields

This is the published version, also available here: http://dx.doi.org/10.1103/PhysRevA.50.5077.We report the discovery of an integrable three-dimensional Hamiltonian system with a velocity-dependent potential. A two-dimensional restriction of that system is (for low frequencies) a good approximation of the motion (in the polarization plane) of the hydrogen atom in circularly polarized microwave fields. An additional integral of motion of the integrable two-dimensional system (being approximate invariant for the hydrogen atom in a circular field) is used in the calculation of the classical ionization field threshold. The result is consistent with all available experimental observations

Ab initio study of the X 2Π and A 2Σ+ states of OH. I. Potential curves and properties

This is the published version, also available here: http://dx.doi.org/10.1063/1.1681891Accurate ab initio CI potential curves and molecular properties are presented for the X 2Π and A 2Σ+ states of OH. Results with known experimental values in parentheses are Re (X 2Π) = 1.841(1.834) bohr, Re (A 2Σ+) = 1.906(1.913) bohr, De (X 2Π) = 4.43(4.63) eV, De (A 2Σ+) = 2.29(2.53) eV, μ(OH,X 2Π,ν=0) = 1.634(1.668) D, and μ(OD,A 2Σ+,ν=0) = 1.861(1.72±0.10) D. Spectroscopic constants calculated from the theoretical potential curves are in satisfactory agreement with experimental results. Other molecular properties studied include quadrupole moments and the electric field gradient at the nuclei

Interaction of Vortices in Complex Vector Field and Stability of a ``Vortex Molecule''

We consider interaction of vortices in the vector complex Ginzburg--Landau equation (CVGLE). In the limit of small field coupling, it is found analytically that the interaction between well-separated defects in two different fields is long-range, in contrast to interaction between defects in the same field which falls off exponentially. In a certain region of parameters of CVGLE, we find stable rotating bound states of two defects -- a ``vortex molecule".Comment: 4 pages, 5 figures, submitted to Phys. Rev. Let

Rapid keratitis and perforation after corneal collagen cross-linking

© 2020 Purpose: To describe a case of rapid keratitis and corneal perforation after epithelium off collagen cross-linking. Observations: We report a case of a 17-year-old male who underwent collagen cross-linking with the protocol and device approved by the United States Food and Drug Administration (FDA) that developed a corneal infiltrate 3 days after the procedure. He later developed corneal thinning and perforation on day 5 requiring the use of cyanoacrylate glue and a Kontur lens. Despite initial improvement in the infiltrate with fortified antibiotics he later had leakage of aqueous around the glue and a flat chamber requiring an emergent penetrating keratoplasty on postoperative day 16. Conclusion and importance: While collagen cross-linking has been very effective for treating keratoconus and is being recommended more frequently since FDA approval in the United States, severe complications such as corneal perforation requiring early transplant can still occur

Acoustic Spectroscopy of the DNA in GHz range

We find a parametric resonance in the GHz range of the DNA dynamics, generated by pumping hypersound . There are localized phonon modes caused by the random structure of elastic modulii due to the sequence of base pairs