Selective control of decoherence is demonstrated for a multilevel system by generalizing the instantaneous phase of any chirped pulse as individual terms of a Taylor series expansion. In the case of a simple two-level system, all odd terms in the series lead to population inversion while the even terms lead to self-induced transparency. These results also hold for multiphoton transitions that do not have any lower-order photon resonance or any intermediate virtual state dynamics within the laser pulse-width. Typeset using REVTEX 1 Minimizing decoherence is an important challenge towards the realization of quantum computing. Nuclear Magnetic Resonance (NMR) spectroscopy of molecules in liquid phase has become an important approach to quantum computing due to their long decoherence times [1]. But it suffers in terms of scalability to larger number of qubits [2], therefore, alternative approaches are being sought [3]. Optical spectroscopy of molecules and nanoparticles could potentially become a highly scalable approach, but for the intramolecular relaxation
Selective control of decoherence is demonstrated for a multilevel system by generalizing the instantaneous phase of any chirped pulse as individual terms of a Taylor series expansion. In the case of a simple two-level system, all odd terms in the series lead to population inversion, while the even terms lead to self-induced transparency. These results also hold for multiphoton transitions that do not have any lower-order photon resonance or any intermediate virtual state dynamics within the laser pulse width. Such results form the basis of a robustly implementable CNOT gate.
The most common method to implement quantum gates is based on the Rabi solution regime of a two-level system excited by external field. There is a very simple reason for this choice. To construct a quantum gate one needs to know the exact form of evolution operator of the qubit under the external excitation. In the case of Rabi solution the qubit evolution has very simple and easily interpreted form. In essence, the whole dynamics of the qubit wave function is governed by the pulse area and it exhibits Rabi oscillations for the time less than the decoherence time. Various implementations of the quantum gates employ relatively weak pulses that results in slow gate operations of order microseconds. To make quantum gates faster one may use strong femtosecond pulses. However, direct implementation schemes are not so obvious because of strong field effects and large bandwidth of the pulses might give rise to unwanted excitations. Here we propose a simple scheme which provides a possibility to utilize strong pulses while keep all advantages of Rabi solution regime. We design fast gates (picosecond time scale) by choosing proper parameters of the chirped pulses as a way to control nonadiabatic terms and to satisfy the adiabaticity conditions. Proposed Hadamard and phase-shift gate allow us to construct universal set of single qubit gates by controlling the effective pulse area and two-photon detuning. The proposed excitation scheme can be used to implement CNOT gate as well.