Quantum coherent control of the lifetime of excited resonance
states with laser pulses
A. García-Vela
Instituto de Física Fundamental, Consejo Superior de Investigaciones Científicas,
C/ Serrano 123, 28006 Madrid, Spain
Introduction: This work explores how to exploit the mechanism of quantum interference occurring between overlapping resonances within a system [1,2] in order to
modify and control the lifetime of a specific excited resonance. The system chosen is the Br2(B,v’)-Ne van der Waals (vdW) cluster, since there has been previously
shown [3,4] that it presents a range of initial v’ vibrational manifolds for which the ground vdW resonance overlaps with other resonances near in energy
corresponding to the v’-1 vibrational manifold (Fig. 1). Thus, modification and control of the predissociation lifetime of the ground vdW resonance of Br2(B,v’)-Ne is
investigated through exact wave packet simulations by creating coherent superpositions of v’ and v’-1 overlapping resonances, following two different control
schemes. In one of them the system is excited with a single laser pulse of varying width in order to change the population of the different overlapping resonances in
the superposition [5]. Two different vibrational states v’ are studied corresponding to the isolated (nonoverlapping) resonance regime, v’=16, and the sparse
overlapping resonance regime, v’=27 (see Fig. 1). The effect of changing the excitation energy (i.e., the center of the wave packet prepared) along the excitation
spectrum of the v’ ground resonance excited (Fig. 2) is also explored as an additional control parameter. In the second control scheme [6] two laser pulses are used
to excite two overlapping resonances, one being the ground resonance of Br2(B,v’=27)-Ne, and the other one being an orbiting resonance in the v=v’-1 manifold. The
delay time and the ratio of intensities between the two excitation pulses are used as control parameters.
Basic equations
Fig.2. Excitation spectra of the Br2(B,v’)-Ne
ground vdW resonance for v’=16 (upper panel) and
v’=27 (lower panels). The three excitation energies
used in the single pulse scheme are indicated by the
arrows in the middle panel. The pulses used in the
two pulse scheme are shown in the lower panel.
Single pulse control scheme. Plot of the lifetimes obtained for different
pulse widths and the three excitation energies using the single pulse
control scheme in the case of v’=27. These lifetimes are collected in the
table along with the lifetimes corresponding to v’=16. In the case of
v’=27 there is a substantial variation of the resonance lifetime due to
interference between the v’ and v’-1 overlapping resonances.
Single pulse control scheme. Survival
probability of the Br2(B,v’)-Ne ground
resonance for v’=16 (exciting the
resonance energy) and v’=27 (exciting an
energy -0.42 cm-1 off resonance) obtained
with different pump pulse widths. For
v’=16 there is practically no change of the
resonance lifetime (about 71 ps, see
TABLE 1) with the pulse width, since
interference is absent. By contrast, for
v’=27 the lifetime increases and an
interference pattern of undulations
appears as the spectral bandwidth of the
pump pulse increases from 200 to 2.5 ps.
Two pulse control scheme. The upper panel shows the Gaussian temporal
profiles of the two pump pulses for different delay times Δt=t2-t1 between
them. The center of one of the pulses is always fixed at t1=0 ps. The lower
panel displays the resonance lifetimes obtained for the ground resonance of
Br2(B,v’=27)-Ne for different delay times and A2/A1 intensity ratios between the
pump pulses. An enhancement of the lifetime by a factor of three is found.
Two pulse control scheme. (a) Survival probabilities calculated for A2=0 (i.e.,
excitation of resonance ψ1 only), and for the delay time Δt=160 ps and the
three intensity ratios A2=0.2A1, A2=0.4A1, and A2=A1. (b) Typical survival
probabilities calculated for several delay times and pulse intensity ratios
along with their corresponding fits used to estimate the resonance lifetime.
The curves have been rescaled for convenience. (c) Survival probabilities
calculated for different delay times in the case of A2=0.4 A1.
Conclusions: Two control schemes are proposed based on the interference effects occurring between overlapping resonances populated in a
coherent superposition. The schemes are applied to a realistic model of the Br2(B,v’)-Ne predissociation dynamics in order to modify and control
the lifetime of the v’=27 ground resonance, which overlaps with orbiting resonances of the v’-1vibrational manifold. In the first control scheme
interference between resonances is controlled by changing the population of the different resonances in the superposition by varying the temporal
width of the pump pulse preparing the superposition state. The second control scheme uses two pump pulses which excite two overlapping
resonances (in the v’ and v’-1 manifolds, respectively). In this scheme two typical experimental parameters like the delay time between the two
pump pulses and their intensities are used as control parameters. While the two schemes provide an extensive degree of control over the
resonance lifetime, the scheme using two pulses exhibits a higher sensitivity of control and a stronger enhancement of the lifetime.
References
[1] E. Frishman and M. Shapiro, Phys. Rev. Lett. 87, 253001 (2001).
[2] P.S. Christopher, M. Shapiro, and P. Brumer, J. Chem. Phys. 123, 064313 (2005).
[3] A. García-Vela and K.C. Janda, J. Chem. Phys. 124, 034305 (2006).
[4] A. García-Vela, J. Chem. Phys. 129, 094307 (2008).
[5] A. García-Vela, J. Chem. Phys. 136, 134304 (2012).
[6] A. García-Vela, J. Phys. Chem. Lett. 3, 1941 (2012).
Acknowledgements: This work was supporteded by CICyT, Ministerio de Ciencia e innovación (MCINN), Spain, Grant No. FIS-2011-29596-C0201, the Consolider program, MCINN, Spain, Grant No. CSD2007-00013, COST Action program, Grant No. CM1002, and the Centro de
Supercomputación de Galicia (CESGA).