Strong decoherence in quantum systems undergoing collisions

Piotr Marecki

Guilherme Fiusa, Gabriel Teixeira Landi

Collision models describe the sequential interactions of a system with independent ancillas. Motivated by recent advances in neutral atom arrays, here we investigate a model where the ancillas are governed by a classical controller that allows them to queue up while they wait for their turn to interact with the system. The ancillas can undergo individual open dynamics while they wait, which could cause them to, e.g., decohere. The system, which plays the role of the server in the queue, can also undergo its own open dynamics whenever it is idle. We show that this framework greatly generalizes existing approaches for quantum collision models, recovering the deterministic and stochastic formulations in the appropriate limits. Next, we show how the combination of queueing dynamics with quantum collisions introduces rich dynamical phenomena, including phase transitions and a sharp dependence on the queue statistics.

Carlos O Reinhold, Marek Seliger, Tatsuya Minami +6 more

A theoretical framework is briefly reviewed that treats the multiple collisions that a quantum system undergoes with particles in its environment. The dynamics is governed by the quantum Lindblad master equation for the density matrix, which can be solved using a Monte Carlo technique. Its classical limit is identified and provides an opportunity to study the role of decoherence in the quantum to classical transition. Applications are discussed related to the dynamics of ions and atoms interacting with solids and gases, and Rydberg wavepackets subject to coloured noise.

Walter T. Strunz

Joyee Ghosh, Rupamanjari Ghosh, Fabienne Goldfarb +2 more

We present a detailed theoretical treatment of a three-level $\ensuremath{\Lambda}$ system in a hot atomic vapor interacting with a coupling and a probe field of arbitrary strengths, leading to electromagnetically induced transparency and slow light under the two-photon resonance condition. We take into account all the relevant decoherence processes including collisions. Velocity-changing collisions (VCCs) are modeled in the strong-collision limit effectively, which helps in achieving optical pumping by the coupling beam across the entire Doppler profile. The steady-state expressions for the atomic density-matrix elements are numerically evaluated to yield the experimentally measured response characteristics. The predictions, taking into account a dynamic rate of influx of atoms in the two lower levels of the $\ensuremath{\Lambda}$, are in excellent agreement with the reported experimental results for ${^{4}\text{H}\text{e}}^{\ensuremath{\ast}}$. The role played by the VCC parameter is seen to be distinct from that by the transit time or Raman coherence decay rate.

Michael B. Mensky