Asymmetric quantum wells

The scheme is illustrated in Fig. 20. In addition to chiral molecules, one can apply this method to two asymmetric quantum wells, to two heteronuclear molecules aligned in an external DC electric field [97]. In the setup of Fig. 20 (lower plot), we consider operating on states i) and their mirror images 1)m by three pulses in a counterintuitive order [92,93], i.e., two pump pulses with Rabi frequencies fl12(0 and fli3(r), which follow a dump pulse H23(0. The Rabi frequencies are defined as, fiy(r) = dtj ij(t)lh — ilij(t) e1 = 0 (0, where dtJ and y(r) are, respectively, the transition dipoles and the envelopes of electric fields, of carrier frequencies a)ij, operating between states i j (i, j = 1,2, 3). If we symmetrically detune the pulse center frequencies, as shown in Fig. 20,... 

Figure 20 (upper plot) An asymmetric quantum well and its mirror image. Also shown are two field-oriented heteronuclear molecules, (lower plot) Illustration of the three pulses used in these CPT systems. The two systems can be discriminated by their different matter-radiation phases 4>. 

A. Tunnelling induced large XPM in an asymmetric quantum wells... 

The purpose of this work is to demonstrate that the techniques of quantum control, which were developed originally to study atoms and molecules, can be applied to the solid state. Previous work considered a simple example, the asymmetric double quantum well (ADQW). Results for this system showed that both the wave paeket dynamics and the THz emission can be controlled with simple, experimentally feasible laser pulses. This work extends the previous results to superlattices and chirped superlattices. These systems are considerably more complicated, because their dynamic phase space is much larger. They also have potential applications as solid-state devices, such as ultrafast switches or detectors. 

Figure 5. Quantum dynamics for an asymmetric double well under coherent or thermal preparations. Vertical energy separation between the two wells (Ae) is 300 cm1, o> = 100...

Figure 41 Left panel calculated 62 first asymmetric peak (- - -) and its Gaussian fit (—) for the (a) Sip]-SiC>2, (b) Si[2]-SiC>2 and (c) S1O2 superlattices. The letter I indicates the interface Gaussian band while the letter Q indicates the bulk-like Gaussian band. Right panel PL spectra of c-Si/Si02 single quantum wells under 488 nm laser excitation at 2 K (a) 1.7 nm, (b) 1.3 nm and (c) 0.6 nm thickness. The asymmetric PL spectra can be fitted by two Gaussian bands, the weak Q band and the strong I band [51],...

Figure 2. A typical realization of a random SO coupling in a quantum well, (a) symmetrically doped, (b) asymmetrically doped well. The parameters are chosen as follows. The concentration of electrons is 5 X 1011 cm 2 as achieved by the one-side doping in Fig.2(b) and symmetric doping in Fig.2(a). The mean SO coupling in Fig.2(b) is (a)0. = 8.5 x 10 1(1 eV-cm, the distance between the dopant layer and the well symmetry plane lo is 10 nm (solid lines) and 20 nm (dashed lines), respectively.

Jordan blocks and (ii) kaon pairs via two coupled Jordan blocks, generated by the CP-violating interaction . If these models carry some actuality in becoming accepted exemplars to arrive at fundamental irreversible formulations of time asymmetric quantum mechanics, then it is our duty to investigate them further. One would then need suitable means and devices to communicate properly with the system, bringing out the essential properties and necessary consequences as well as predicting additional features and associated behaviour. 

This section considers a single asymmetric double-well potential. At low temperatures a quantum mechanical description is necessary, and only the lowest energy eigenstates will be relevant. If the energy asymmetry of the wells is not too great then it will be sufficient to describe the problem in terms of a two-state basis, where the two states are localized in each of the two wells of the potential. These two states compose the TLS. 

We propose an asymmetric double AlGaAs/GaAs quantum well strueture with a eommon continuum to generate a large cross-phase modulation (XPM). The basie idea is to combine resonant tuimeling induced constructive interference in eross-phase modulation (XPM) and tunneling-induced transparency (TIT). The band structure is shown in Fig. 11, whieh is designed with small electron decay rates, which can reduce the linear absorption effectively. A... 

Figure 11 Conduction subband of the asymmetric double quantum well.

The spin-boson model can be motivated in terms of the physical problan of a quantum particle (e.g., an electron, muon, or proton) tunneling in an asymmetric double well (Figure 11.4). The relevant energy scales are the asymmetry he, tunneling HAq, and thermal k T, which can be all comparable but are much smaller than the barrier height Eq. Under this circumstance, the dynamics of the quantum particle moving in the double well can be described by what we shall refer to as the subsystem Hamiltonian... 

Figure12.15 (a) High-magnification XTEM image showing the sharpness and abruptness of quantum-well interfaces (b) low magnification image showing the generation of defects in MQWs. The encircled region shows an asymmetric V-defect .

At higher pressures only Raman spectroscopy data are available. Because the rotational structure is smoothed, either quantum theory or classical theory may be used. At a mixture pressure above 10 atm the spectra of CO and N2 obtained in [230] were well described classically (Fig. 5.11). For the lowest densities (10-15 amagat) the band contours have a characteristic asymmetric shape. The asymmetry disappears at higher pressures when the contour is sufficiently narrowed. The decrease of width with 1/tj measured in [230] by NMR is closer to the strong collision model in the case of CO and to the weak collision model in the case of N2. This conclusion was confirmed in [215] by presenting the results in universal coordinates of Fig. 5.12. It is also seen that both systems are still far away from the fast modulation (perturbation theory) limit where the upper and lower borders established by alternative models merge into a universal curve independent of collision strength. 

Quadrupolar nuclei Those nuclei, which because of their spin quantum number (which is always >1/2), have asymmetric charge distribution and thus posses an electric quadrupole as well as a magnetic dipole. This feature of the nucleus provides an extremely efficient relaxation mechanism for the nuclei themselves and for their close neighbors. This can give rise to broader than expected signals. 

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