Creation Of Coherent Superposition States Research Articles

Speeding up the creation of coherent superposition states by shortcut-to-adiabaticity means

We propose protocols of loop stimulated Raman shortcut-to-adiabatic passage (STIRSAP) and modified-STIRSAP to speed up the creation of arbitrary high fidelity coherent superposition states (F≃0.999). In loop- and modified-STIRSAP protocols, the nonadiabatic coupling between the dark and bright states can be canceled by an additional microwave pulse and modified pump and Stokes pulses, respectively. As a result of dark state rotation, the creation of preselected coherent superposition states can be achieved beyond the adiabatic limit. Compared with the stimulated Raman adiabatic passage (STIRAP) protocol, the evolution time of the creation of coherent superposition states can be shortened. Our numerical calculations agree well with the theoretical analysis in the partial dressed-state picture.

Tunneling-assisted coherent population transfer and creation of coherent superposition states in triple quantum dots

A scheme is proposed for coherent population transfer and creation of coherent superposition states assisted by one time-dependent tunneling pulse and one time-independent tunneling pulse in triple quantum dots. Time-dependent tunneling, which is similar to the Stokes laser pulse used in traditional stimulated Raman adiabatic passage, can lead to complete population transfer from the ground state to the indirect exciton states. Time-independent tunneling can also create double dark states, resulting in the distribution of the population and arbitrary coherent superposition states. Such a scheme can also be extended to multiple quantum dots assisted by one time-dependent tunneling pulse and more time-independent tunneling pulses.

Multiphoton resonant excitation of Fermi-Dirac sea in graphene at the interaction with strong laser fields

In order to develop the microscopic theory of the multiphoton interaction of graphene with strong laser fields of arbitrary polarization, the analytical solution of established evolutionary equation for graphene single-particle density matrix was obtained revealing the generalized Rabi oscillations of Fermi-Dirac sea in the graphene. Creation of coherent superposition states of the particle-hole pairs in the graphene at the multiphoton resonant excitation by laser pulses of arbitrary polarizations and harmonics generation at the particle-hole annihilation from these superposition states are shown.

Creation of coherent superposition states in inhomogeneously broadened media with relaxation

We propose and analyze a scheme for "on demand" creation of coherent superposition of meta-stable states in a tripod-structured atom using frequency-chirped laser pulses. Negligible excitation of the atoms during the creation of the superposition states is a priority in our consideration. The underlying physics of the scheme is explained using the formalism of adiabatic states. By numerically solving master equation for the density matrix operator, we analyze the influence of the spontaneous decay and transverse relaxation on the efficiency of the creation of superposition states. We show that the proposed scheme is robust against small-to-medium variations of the parameters of the laser pulses. We provide a detailed analysis of the effect of the inhomogeneous (Doppler-) broadening on the efficiency of the coherence creation and show that the proposed scheme may be equally efficient in both homogeneously and Doppler-broadened media.

Creation of Coherent Superposition States in Multilevel Systems

A powerful approach to generate multilevel superpositionstate in ∧-type manifold of levels is proposed. In the analysis, weintroduce a group of rotations to transform the coupled system to a simplerform, which involves one coupled and several decoupled, dark states in theground state manifold. Then an arbitrary superposition state of initial andfinal states can be created. In particular, when the Rabi frequencies of theStokes pulses have equal magnitudes, a superposition state (equal populationof the (n−2) superposition states) will be generated. A numerical simulationof coherence generation is given. It is shown that a small transientpopulation in metastable state decreases as the intensity of Stokes pulsesincreases. Experimental implementation in Neon atom is given.

Creation of coherent superposition states in hydrogenlike ions via multiphoton resonant excitation

On the basis of the analytical solution of the Dirac equation the resonant multiphoton excitation of highly charged hydrogenlike ions in a strong high-frequency laser field is investigated. It is shown that the dynamics of the relativistic system is equivalent to two independent four-level systems (in the electrical-dipole approximation). The time evolution of the system is found using the nonperturbative resonant approach. We predict that due to multiphoton excitation by an appropriate laser pulse one can achieve various coherent superposition states in atomic or ionic systems with a high nuclear charge.

Adiabatic creation of coherent superposition states in atomic beams

We describe a technique for creating superpositions of degenerate quantum states, such as are needed for beam splitters used in matter-wave optics, by manipulating the timing of three orthogonally polarized laser beams through which moving atoms (or molecules) pass; motion across the laser beams produces pulses in the atomic rest frame. As illustrated with representative simulations for transitions in metastable neon, a single pass through three overlapping laser beams can produce superpositions (with preselected phase) of atomic beams differing by transverse momentum corresponding to the momentum of four photons. Like the two-photon momentum transfer of the tripod linkage pattern which it extends, the method relies on controlled adiabatic time evolution in the Hilbert subspace of two degenerate dark states. It is thus a generalization to multiple dark states (and larger transfers of linear momentum to the atomic beam) of the single dark state occurring with the stimulated Raman adiabatic passage (STIRAP) technique, and therefore it is potentially insensitive to decoherence due to spontaneous emission. By extending the tripod-linkage system to more numerous degenerate states, the technique not only increases the atomic beam deflections but, as we demonstrate, allows control over the superposition phase and amplitudes. LIke other techniques based on adiabatic time evolution, the technique is robust with respect to variations of the intensity, timing, and other characteristics of the laser fields. Unlike STIRAP, the same robust partial population transfer occurs for opposite timings of the pulse sequence, as is needed for such procedures as Hadamard gates.

Adiabatic creation of coherent superposition states via multiple intermediatestates

We consider an adiabatic population transfer process that resembles the well-establishedstimulated Raman adiabatic passage. In our system, the states have nonzero angularmomentums J,therefore, the coupling laser fields induce transitions between the magnetic sublevelsof the states. In particular, we discuss the possibility of creating coherentsuperposition states in a system with coupling pattern J = 0 ⇔ 1 and 1 ⇔ 2. Initially, thesystem is in the J = 0state. We show that by, applying two delayed overlapping laser pulses, it is possibleto create any final superposition state of the magnetic sublevels |2, −2⟩, |2, 0⟩, |2, +2⟩.Moreover, we find that the relative phases of the applied pulses influence not onlythe phases of the final superposition state but also the probability amplitudes. Weshow that if we fix the shape and the time delay between the pulses, the finalstate space can be entirely covered by varying the polarizations and relativephases of the two pulses. Performing numerical simulations we find that ourtransfer process is nearly adiabatic for the whole parameter set.