Shih-I Chu

Efficient many-party controlled teleportation of multiqubit quantum information via entanglement

We present a way to teleport multiqubit quantum information from a sender to a distant receiver via the control of many agents in a network. We show that the original state of each qubit can be restored by the receiver as long as all the agents collaborate. However, even if one agent does not cooperate, the receiver cannot fully recover the original state of each qubit. The method operates essentially through entangling quantum information during teleportation, in such a way that the required auxiliary qubit resources, local operation, and classical communication are considerably reduced for the present purpose.

Possible realization of entanglement, logical gates, and quantum-information transfer with superconducting-quantum-interference-device qubits in cavity QED

We present a scheme to achieve maximally entangled states, controlled phase-shift gate, and SWAP gate for two superconducting-quantum-interference-device (SQUID) qubits, by placing SQUIDs in a microwave cavity. We also show how to transfer quantum information from one SQUID qubit to another. In this scheme, no transfer of quantum information between the SQUIDs and the cavity is required, the cavity field is only virtually excited and thus the requirement on the quality factor of the cavity is greatly relaxed.

Theoretical study of multiple high-order harmonic generation by intense ultrashort pulsed laser fields: A new generalized pseudospectral time-dependent method

Abstract We present a new time-dependent method for accurate and efficient non-perturbative treatment of multiple high-order harmonic generation (HHG) in intense laser fields. The time development of the wavefunction is obtained by a new split-operator time-propagation technique in the energy representation. The generalized pseudospectral technique is extended to perform an optimal spatial grid discretization, leading to significant improvement of the quality of the wavefunction over that obtained by the equal-spacing spatial discretization techniques. The accuracy of the method is demonstrated by several benchmark calculations including the excellent agreement of the HHG power spectra in length and acceleration forms. The method is applied to a detailed study of the coherent control of HHG spectra of atomic hydrogen in intense ultrashort pulsed laser fields with or without the chirp. Several novel chirp-dependent and pulse-duration-dependent phenomena are predicted. Comparison with available experimental observation is made.

Ab initio study of the X2Π and A2Σ+ states of OH. I. Potential curves and properties

Accurate ab initio CI potential curves and molecular properties are presented for the X2Π and A2Σ+ states of OH. Results with known experimental values in parentheses are Re(X2Π) = 1.841(1.834) bohr, Re(A2Σ+) = 1.906(1.913) bohr, De(X2Π) = 4.43(4.63) eV, De(A2Σ+) = 2.29(2.53) eV, μ(OH,X2Π,ν=0) = 1.634(1.668) D, and μ(OD,A2Σ+,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.

Semiclassical many-mode floquet theory

Abstract It is shown that the single-mode Floquet formalism of Shirley can be extended to a generalized many-mode Floquet theory, yielding a practical non-perturbative technique for the semiclassical treatment of the interaction of a quantum system several monochromatic oscillating fields. The theory is illustrated by a detailed study of the population dynamics of a three-level system driven by two monochromatic radiation fields.

Sub-cycle Oscillations in Virtual States Brought to Light

Understanding and controlling the dynamic evolution of electrons in matter is among the most fundamental goals of attosecond science. While the most exotic behaviors can be found in complex systems, fast electron dynamics can be studied at the fundamental level in atomic systems, using moderately intense (≲103 W/cm2) lasers to control the electronic structure in proof-of-principle experiments. Here, we probe the transient changes in the absorption of an isolated attosecond extreme ultraviolet (XUV) pulse by helium atoms in the presence of a delayed, few-cycle near infrared (NIR) laser pulse, which uncovers absorption structures corresponding to laser-induced “virtual” intermediate states in the two-color two-photon (XUV+NIR) and three-photon (XUV+NIR+NIR) absorption process. These previously unobserved absorption structures are modulated on half-cycle (~1.3 fs) and quarter-cycle (~0.6 fs) timescales, resulting from quantum optical interference in the laser-driven atom.

Laser-induced molecular stabilization and trapping and chemical bond hardening in intense laser fields

Abstract We study the intensity-dependent behavior of laser-induced vibrational quasi-energy (VQE) resonance structure and photodissociation rates of H 2 + molecular ions in intense laser fields at 775 nm and report a novel new high-intensity phenomenon. At strong fields, the vibrational levels are shifted and broadened substantially and break into several separate VQE resonance groups. distortion of the internuclear potential by the fields leads to the formation of various (field-dressed) adiabatic potential wells near multiphoton resonances which can support long-lived resonance states. The most striking finding is that high-lying VQE resonance states can in fact become more stabilized and longer lived at higher laser intensities, a phenomenon which may be termed as “bond hardening”. Time-dependent calculations confirm the laser-induced stabilization phenomenon and reveals that molecular population may be trapped simultaneously in different potential wells, at different internuclear separations (multiple well trapping).

Complex quasivibrational energy formalism for intense‐field multiphoton and above‐threshold dissociation: Complex‐scaling Fourier‐grid Hamiltonian method

We present a new complex‐scaling Fourier‐grid Hamiltonian (CSFGH) method for accurate and efficient determination of laser‐induced (multichannel) molecular resonance states without the use of basis set expansions. The method requires neither the computation of potential matrix elements nor the imposition of boundary conditions, and the eigenvectors provide directly the values of the resonance wave functions at the space grid points. The procedure is particularly valuable for excited‐state problems where basis set expansion methods face the challenge. The simplicity and usefulness of the CSFGH method is demonstrated by a case study of the intensity‐dependent complex quasivibrational energy eigenvalues (ER, −Γ/2) and eigenvectors associated with multiphoton and above‐threshold dissociation of H+2 ions in the presence of intense laser fields (I=1012–1014 W/cm2 ).

Studies of rotational predissociation of van der Waals molecule by the method of complex coordinate

A practical method is presented for calculating resonance energies and widths (lifetimes) of metastable states of van der Waals molecules, incorporating the use of complex coordinate transformation and square‐integrable basis functions. The utility of the method is illustrated through a study of the level widths and energies of rotationally predissociating atom–diatom model systems. Satisfactory agreement with previous works was found. Besides involving only bound state calculations and being free from imposement of boundary conditions, the method can be readily extendable to multichannel coupling problems.

Energy deposition in SO2 via intense infrared laser multiphoton excitation

Abstract The feasibility of multiphoton excitation (MPE) and dissociation (MPD) of triatomic molecules is the subject of current experimental controversy. The most probable path approximation (MPPA) makes use of artificial intelligence algorithms to select the most important excitation paths within the semiclassical Floquet matrix, allowing efficient and accurate calculation of non-linear MPE quantum dynamics to very high order. An ab initio study of SO 2 using the MPPA indicates that collisionless MPD will not be achieved at laser field strengths under 20 GW/cm 2 . The possibility of MPD at higher laser intensities is currently under investigation.