Wireless adiabatic power transfer

We propose a technique for efficient mid-range wireless power transfer between two coils, by adapting the process of adiabatic passage for a coherently driven two-state quantum system to the realm of wireless energy transfer. The proposed technique is shown to be robust to noise, resonant constraints, and other interferences that exist in the neighborhood of the coils.     

Flow field mapping by multi-zone adiabatic passage excitation

This paper describes a robust method for flow field mapping by multi-zone adiabatic fast passage (AFP). It provides a quick and simple way to simultaneously acquire flow profiles at several locations and arbitrary orientations inside the field-of-view. The flow profile is the time-averaged evolution of the labeled flowing material. Results obtained using a carotid bifurcation and jet phantoms are similar to the previous experimental studies employing Laser Doppler Anemometry (LDA), and other flow visualization techniques. In addition, the preliminary results abtained with a human volunteer support the feasibility of the technique for in vivo flow quantification.     

Generation of atomic entangled states in a bi-mode cavity via adiabatic passage

We propose schemes to prepare atomic entangled states in a bi-mode cavity via stimulated Raman adiabatic passage (STIRAP) and fractional stimulated Raman adiabatic passage (f-STIRAP) techniques. Our scheme should be realizable in the near future because of the existence of all experimental ingredients. Our numerical simulation shows we can entangle the atoms with high fidelities by choosing proper laser pulses.     

Dependence of adiabatic population transfer on pulse profile

Control of population transfer by rapid adiabatic passage has been an established technique wherein the exact amplitude profile of the shaped pulse is considered to be insignificant. We study the effect of ultrafast shaped pulses for two-level systems, by density-matrix approach. However, we find that adiabaticity depends simultaneously on pulse profile as well as the frequency modulation under non-resonant conditions     

Condition for adiabatic passage in the earth’s-field NMR technique

The equation of motion dM/dt=γ M×B(t) is solved for the case B(t)=jB_p(t)+kB_e. The field B_e is a small static field, typically the earth’s field. The field B_p(t) decays exponentially toward zero with time constant T. This decay is produced by an overdamped switching transient that occurs near the end of the rapid cutoff of the coil current used to polarize the sample. It is assumed that B_p is initially large compared to B_e, and that magnetization M is initially along the resultant field B. Exact solutions are obtained numerically for several decay time constants of B_p, and the motion of M is depicted graphically. It is found that for adiabatic passage, the final cone angle β of the precession in field B_e is related to the decay time constant of B_p by β=2e^{−(π/2)ω_eT}. This is confirmed by measurements of the amplitudes of the ensuing free-precession signals for various decay rates of B_p. Near-perfect adiabatic passage (magnetization aligned within 2° of the earth’s field) can be achieved for time constants T2.6/ω_e. For the case of sudden passage, an approximate analytic solution is developed by linearizing the equation of motion in the laboratory frame of reference. For the adiabatic case, an approximate analytic solution is obtained by linearizing the equation of motion in a rotating frame of reference that follows the resultant field B=B_p+B_e.     

Calculated T1 images derived from a partial saturation-inversion recovery pulse sequence with adiabatic fast passage

Calculated T1 images of the head and abdomen have been obtained using an alternating partial saturation-inversion recovery pulse sequence. Timing parameters were adjusted to yield optimum T1 contrast-to-noise ratio for this sequence for the range of T1 studied. Adiabatic fast passage (AFP) was implemented for the nonselective inverting pulse, to reduce the sensitivity of the measurement to RF and static field inhomogeneity. A nonlinear frequency sweep was used to improve the efficiency of the AFP pulse. The effect on the T1 calculation of slice selection during the pi/2 pulses was also determined and corrected for in the image reconstruction algorithm. The T1's determined by this method show a standard deviation of less than 10%, and good agreement with the literature.     

Tunneling-induced coherent electron population transfer in an asymmetric quantum well

We propose an asymmetric double quantum wells structure with a common continuum and investigate the effect of resonant tunneling on the control of coherent electron population transfer between the two quantum wells. By numerically solving the motion equations of element moments, the almost complete electron population transfer from the initial subband to the target subband could be realized due to the constructive interference via flexibly adjusting the structure parameters.     

Coherent population transfer in an atom by multiphoton adiabatic rapid passage

Coherent population transfer in an atom using a sequence of adiabatic rapid passages through single-photon resonances is well-known, but it requires that the frequency sweep match the changing frequencies of the atomic transitions. The same population transfer can be effected via a single multiphoton adiabatic rapid passage, which requires only a small frequency sweep, if it is possible to select the desired multiphoton transition from the many possible transitions. Here we report the observation of population transfer between Rydberg states by high order multiphoton adiabatic rapid passage.     

Optimised adiabatic fast passage spin flipping for He neutron spin filters

We describe here a method of performing adiabatic fast passage (AFP) spin flipping of polarized ³He used as a neutron spin filter (NSF) to polarize neutron beams. By reversing the spin states of the ³He nuclei the polarization of a neutron beam can be efficiently reversed allowing for the transmission of a neutron beam polarized in either spin state. Using an amplitude modulated frequency sweep lasting 500 ms we can spin flip a polarized ³He neutron spin filter with only 1.8×10⁻⁵ loss in ³He polarization. The small magnetic fields (10-15 G) used to house neutron spin filters mean the ³He resonant frequencies are low enough to be generated using a computer with a digital I/O card. The versatility of this systems allows AFP to be performed on any beamline or in any laboratory using ³He neutron spin filters and polarization losses can be minimised by adjusting sweep parameters.     

Generation of four-atom Greenberger-Horn-Zeilinger state via adiabatic passage

We propose a scheme to generate a Greenberger-Horn-Zeilinger (GHZ) state of four atoms trapped in a two-mode optical cavity via an adiabatic passage. The scheme is robust against moderate fluctuations of the experimental parameters. Numerical calculations show that the excited probabilities of both the cavity modes and the atoms are tiny and depend on the pulse peaks of the classical laser fields. For certain decoherence due to the atomic spontaneous emission and the cavity decay, there exits a range of pulse peaks to get a high fidelity.     

Acceleration of adiabatic quantum state transfer in a spin chain under zero-energy-change pulse control

We present a protocol for accelerating adiabatic quantum state transfer through a spin chain by adding an effective control pulse. Using Feshbach P-Q partitioning technique, we obtain the one-component dynamical equation which guides us to set the amplitude and period of the control field. This field can be a sequence of alternatively negative and positive (zero-energy change) pulses which can be realized easily in experiment. As an example, we discuss a three particles spin chain and the numerical calculation shows that the accelerated quantum state transfer can be obtained.     

Quantum Information in the Frame of Coherent States Representation

In this paper we have showed that the qubit can be expressed through the coherent states. Consequently, a message, i.e. a sequence of qubits, is expressed as a tensor product of coherent states. In the quantum information theory and practice, only the code and key message are expressed as a sequence of qubits, i.e. through a quantum channel, the properly information will be transmitted by using a classical channel. Even if the most used coherent states in the quantum information theory are the coherent states of the harmonic oscillator (particularly, expressing by them the Schrödinger “cat states” and the Bell states), several authors have been demonstrated that other kind of coherent states may be used in quantum information theory. For the ensembles of qubits, we must use the density operator, in order to describe the informational content of the ensemble. The diagonal representation of the density operator, in the coherent state representation, is also useful to examine the entanglement of the states.     

Coherent control via interplay between driving field and two-body interaction in a double well

We investigate interplay between external field and interatomic interaction and its applications to coherent control of quantum tunneling for two repulsive bosons confined in a high-frequency driven double well. By using a full solution which is generated analytically as a coherent non-Floquet state, three kinds of the stationary-like states (SLSs) with different degeneracies are illustrated, which corresponding to the different coherent destructions of tunneling (CDT) at the Floquet level-crossing, avoided-crossing and uncrossing points. The analytical results are numerically confirmed and perfect agreements are found. Based on the results, a useful scheme of quantum tunneling switch between the SLSs is presented.     

Deterministic generation of Greenberger-Horne-Zeilinger and W states for three distant atoms via adiabatic passage

We propose two schemes for generating Greenberger-Horne-Zeilinger and W states of three distant atoms.In the present schemes,the atoms are individually trapped in three spatially separated optical cavities coupled by two optical fibres.Performing an adiabatic passage along dark states,the population of cavities and fibres excited is negligible under certain conditions.In addition,the spontaneous decay of atoms is also efficiently suppressed based on our proposals.Furthermore,the discussion about the entanglement fidelity is given and we point out that our schemes work robustly with small fluctuations of experimental parameters.     

Deterministic generation of entangled photons by cavity-assisted interactions through adiabatic passage

We propose a deterministic scheme for generation of highly entangled photon states using a high-Q two-mode optical cavity and the dark state evolution. Because of the adiabatic operation, our proposal is robust to ambient noise, and the relevant dynamics is insensitive to the randomness of moderate fluctuations regarding experimental parameters. Our scheme not only works deterministically, but also has the advantage of achieving highly entangled photons by adiabatically increasing or decreasing the Rabi frequencies regarding the classical driving pulses, which would be practical in real implementation. Our scheme can also be extended to generation of multiphoton entanglement.     

Adiabatic population transfer in the three-level Λ-system: two-photon lineshape

We discuss the dependence of the population transfer probability in the three-level Λ-scheme using stimulated Raman adiabatic passage on detuning from the two-photon resonance. For a large decay rate of the intermediate level we found that the two-photon lineshape is close to Gaussian with linewidth inversely proportional to the square root of the decay rate. The shift of the maximum of the two-photon line from exact two-photon resonance has been investigated.     

General theory of population transfer by adiabatic rapid passage with intense, chirped laser pulses

We present a general theory of adiabatic rapid passage (ARP) with intense, linearly chirped laser pulses. For pulses with a Gaussian profile and a fixed bandwidth, we derive a rigorous formula for the maximum temporal chirp rate that can be sustained by the pulse. A modified Landau-Zener formula displays clearly the relationships among the pulse parameters. This formula is used to derive the optimal conditions for efficient, robust population transfer. As illustrations of the theory, we present results for two- and four-level systems, and selective vibronic excitation in the I₂ molecule. We demonstrate that population transfer with chirped pulses is more robust and more selective than population transfer with transform-limited pulses. Received 6 September 2000 and Received in final form 25 September 2000     

Quantum Superdense Coding Based on Coherent States in Cavity QED

A physical scheme for the implementation of quantum superdense coding has been proposed in Cavity QED. The detuned interaction between Λ-type three-level atoms and coherent fields constitute the main superdense coding process. The quantum superdense coding can be realized in an easier way, and the atoms are not excited during the whole process, so the effect of atomic decay is eliminated naturally.     

Barut-Girardello Coherent States for the Parabolic Cylinder Functions

The Barut-Girardello coherent states for the parabolic cylinder functions are constructed. It is shown that the resolution of unity condition is satisfied for the coherent states. In the Hilbert space spanned by the parabolic cylinder eigenstates, the appropriate measure is also obtained.