Coherence lifetime

Here we describe the development of the coherent-control toolbox with gas-phase iodine molecules [37 1, 48]. The gas-phase molecules are isolated from each other, so that they have long coherence lifetime, serving as an ideal platform to observe and control quantum coherence. First, we describe our experiments to observe and control the temporal evolution of the WP interference. Second, the eigenstate picture of the WP interference is presented. Finally, we demonstrate the application of WPI to ultrafast molecular computing. 

The concept of coherent control, which we have developed with isolated molecules in the gas phase, is universal and should apply to condensed matter as well. We anticipate that the coherent control of wave functions delocalized over many particles in solids or liquids will be a useful tool to track the temporal evolution of the delocalized wave function modulated by many-body interactions with other particles surrounding itself. We may find a clue to better understand the quantum-classical boundary by observing such dynamical evolution of wave functions of condensed matter. In the condensed phase, however, the coherence lifetime is in principle much shorter than in the gas phase, and the coherent control is more difficult accordingly. In this section, we show our recent efforts to develop the coherent control of condensed matter. 

To add further credence to these critical assignments, the polarization-depen-dent OODR(Si) spectrum was recorded for the Ojj and 6j bands with implement of photoelastic modulator (PEM). This device alters the polarizations of the probe and pump beams with each laser pulse in a shot-by-shot fashion. For the 0q transition, the two beams would have parallel polarizations (pump and probe transition are both y (B2) polarized). For the 6j transition, the two photons would be perpendicularly polarized to each other, with y and z polarization, respectively. The temporal profiles of polarization-dependent OODR spectra in Figure 2.25 show the expected behavior, where the signals of the parallel and perpendicular polarizations for the S2(0°) < S [ (41) < S0(Oo) and S2(61) <— SjtT1) <— So(0o) are plotted against the delay time. The effects of reversing the polarizations is not too pronounced in these experiments, as the rotational coherence lifetimes are very short and the overall rotation of the molecule quickly scrambles the polarizations of the signals. At very short delay... 

Soon after the report of de Vries and Wiersma" that at low temperature the coherence lifetime in Sj -So electronic transitions of organics could approach the fluorescence lifetime, Aartsma and Wiersma succeeded in detecting the first photon echo in an organic solid. The experiment was done at the S, <-S o transition of pyrene in biphenyl and is a beautiful illustration of the possible difference between optical T, and 7. In Fig. 13 we reproduce the absorption spectrum of pyrene in the origin region, which may be identified as a T -spectrum, and a photon-echo excitation spectrum, which may be called a 72-spectrum. The different lines in the... 

In spite of impressive experimental demonstrations of basic quantum information effects in a number of different mesoscopic solid state systems, such as quantum dots in semiconductor microcavities, cold ions in traps, nuclear spin systems, Josephson junctions, etc., their concrete implementation is still at the proof-of-principle stage [1]. The development of materials that may host quantum coherent states with long coherence lifetimes is a critical research problem for the nearest future. There is a need for the fabrication of quantum bits (qubits) with coherence lifetimes at least three-four orders of magnitude longer than it takes to perform a bit flip. This would involve entangling operations, followed by the nearest neighbor interaction over short distances and quantum information transfer over longer distances. 

J.R. Lewandowski, J.-N. Dumez, U. Akbey, S. Lange, L. Etnsley, H. Oschkinat, Enhanced resolution and coherence lifetimes in the sohd-state NMR spectroscopy ofper-deuterated proteins under ultrafast magic-angle spinning, J. Phys. Chem. Lett. 2 (2011) 2205-2211. 

Two main approaches to the control of molecules using wave interference in quantum systems have been proposed and developed in different languages . The first approach (Tannor and Rice 1985 Tannor et al. 1986) uses pairs of ultrashort coherent pulses to manipulate quantum mechanical wave packets in excited electronic states of molecules. These laser pulses are shorter than the coherence lifetime and the inverse rate of the vibrational-energy redistribution in molecules. An ultrashort pulse excites vibrational wave packets, which evolve freely until the desired spacing of the excited molecular bond is reached at some specified instant of time on a subpicosecond timescale. The second approach is based on the wave properties of molecules as quantum systems and uses quantum interference between various photoexcitation pathways (Brumer and Shapiro 1986). Shaped laser pulses can be used to control this interference with a view to achieving the necessary final quantum state of the molecule. The probability of production of the necessary excited quantum state and the required final product depends, for example, on the phase difference between two CW lasers. Both these methods are based on the existence of multiple interfering pathways from the initial... 

Yi2 Now t, the effective coherence lifetime of Pj2> depends on the experimental situation. Without going into the... 

Fig. 7 Spinning speed dependence of H MAS spectra of (a-c) Cu(DL-Ala)2 (H20) and (d-f) Mn (acac)3. The spectra were obtained at H frequency of 400.2 MHz with 1-pulse excitation and a rotor synchronous echo. Reprinted with permission from [31]. 2005 American Chemical Society. Spiiming speed dependence of H MAS spectra of (a) Fe-DIAD (S = 2) and (b) Tb (DPM)3 (/ = 6). The spectra were obtained at H frequency of 500 MHz with 1-pulse excitation and a rotor synchronous echo. Reprinted with permission from [26, 27], 2006 and 2007 American Chemical Society, (c) Spinning speed dependence of the H coherence lifetimes, measured with a CPMG sequence with adiabatic pulse trains (see Sect. 3.3)...

In solids, these centers (typically, Co ", Fe , Ln ) enhance significantly the longitudinal relaxation of the surrounding spins, but have a negligible effect both on their observed linewidths and on the coherence lifetimes, and do not significantly reduce the efficiency of magnetization transfer. In these conditions, dipolar-based experiments optimized for the fast MAS regime (double quantum CP [33, 34] or... 

Kervem G, Sleuemagel S, Engelke F, Pintacuda G, Emsley L (2007) Absence of curie relaxation in paramagnetic solids yields long HI coherence lifetimes. J Am Chem Soc 129 14118-14119... 

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