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ACTA PHOTONICA SINICA

Two-qubit Quantum State Controlled by Ultra-short Pulse

Xiangyang Yu

Published Jan 1, 2009• 0 citations
OpenAlex

Abstract

The semi-classical theory of the interaction between light and matter was applied to the study of the interaction of ultra-short pulse with the two two-level system.A comparison was made between the independent double path-ways(IDPW)and the coherent double path-ways(CDPW)driven in different ways.It is suggested that compared with single qubit,the two-qubits shows a higher property of coherence when interacted with the ultra-short pulse.This property of coherence is related to the initial state of the system,the detuning,and the driving path-ways.And,it is demonstrated that with the presented model quantum state operation can be made through the modulation of the pulse area.

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The semi-classical theory of the interaction between light and matter was applied to the study of the interaction of ultra-short pulse with the two two-level system.A comparison was made between the independent double path-ways(IDPW)and the coherent double path-ways(CDPW)driven in different ways.It is suggested that compared with single qubit,the two-qubits shows a higher property of coherence when interacted with the ultra-short pulse.This property of coherence is related to the initial state of the system,the detuning,and the driving path-ways.And,it is demonstrated that with the presented model quantum state operation can be made through the modulation of the pulse area.
Within the framework of semi-classical theory of light and matter, we investigate the entanglement dynamics of the bipartite system consisting of two identical and interacting two-level atoms in QED by use of concurrence, which are driven by coherent double ultra-short laser pulses divided by diverse phase differences. Results show that under different detuning, the phase difference can exert significant influence on the entanglement evolution, such as delaying or accelerating entanglement sudden death (ESB) and revival (ESR). Furthermore, with the increment of detuning, ESD and ESR disappear irrespective of various phase differences.
We consider a double two-level system in which each single two-level system is driven by a strong pulse. The light shifts induced by the strong field are probed by a weak pulse that connects the two sub-system in a crossed manner connecting the ground state of one system with the excited state of the other and vice versa. We are interested in coherent control of medium gain for the weak pulse and we demonstrate the conditions on laser and atomic parameters that render this control possible. Both ultra-short and long pulse regimes are discussed
Based on the semi-classical theory of the interaction between light and matter, we propose an effective scheme for describing the realization of single quantum gates. The rigorous analytical solution for the resonant system, in which the double ultra-short powerful laser pulses with accurately controllable relative phase difference will interact with the atoms, is obtained by solving the time-dependent Schrödinger equation. According to the corresponding solution, we deduce the systematic matrix expression of unitary transformation. Universal quantum logic gates are all implemented theoretically by means of regulating properly the laser pulses' intensity and its relative phase difference as well as the optic detuning. This method also proves practical in terms of its comparably easier manipulation.
We develop a coherent control theory for multimode quantum light. It allows us to examine a fundamental problem in quantum optics: what is the optimal pulse form to drive a two-photon-transition? In formulating the question as a coherent control problem, we show that—and quantify how much—the strong frequency quantum correlations of entangled photons enhance the transition compared to shaped classical pulses. In ensembles of collectively driven two-level systems, such enhancement requires nonvanishing interactions.
The pulse control of dephasing is studied for a two-level quantum system (qubit) interacting with a quantum environment. It has been shown that dephasing in a qubit due to qubit–environment interactions can be suppressed by a sequence of periodic π pulses with infinitely short duration. To study how the effectiveness of the pulse control is affected by finite pulse duration t d , we calculate the time evolution of the reduced density operator for a qubit under a sequence of π pulses. We show that the pulse control is effective even for not short t d if a suitable pulse sequence is adopted.
Starting from famous Schrödinger equation within the framework of semi-classical theory of light-matter interaction, we firstly obtain the analytical non-resonant solutions of the driven bipartite system's entanglement dynamics in independent and coherent double pathways. Numerical simulations show that under non-resonant condition, entanglement sudden death and revival between these transition patterns behave quite differently, indicating the utmost importance of transition pathways' interference. Furthermore, the laser pulse's area and detuning exert significant but quite distinct influences on the entanglement dynamics. Our analyses are helpful in manipulating entanglement in current experimental technology.