Collective decoherence of cold atoms coupled to a Bose–Einstein condensate

Abstract

We examine the time evolution of cold atoms (impurities) interacting with an environment consisting of a degenerate bosonic quantum gas. The impurity atoms differ from the environment atoms, being of a different species. This allows one to superimpose two independent trapping potentials, each being effective only on one atomic kind, while transparent to the other. When the environment is homogeneous and the impurities are confined in a potential consisting of a set of double wells, the system can be described in terms of an effective spin-boson model, where the occupation of the left or right well of each site represents the two (pseudo)-spin states. The irreversible dynamics of such system is here studied exactly, i.e., not in terms of a Markovian master equation. The dynamics of one and two impurities is remarkably different in respect of the standard decoherence of the spin -boson system. In particular we show: (i) the appearance of coherence oscillations, (ii) the presence of super and sub decoherent states which differ from the standard ones of the spin boson model, and (iii) the persistence of coherence in the system at long times. We show that this behaviour is due to the fact that the pseudospins have an internal spatial structure. We argue that collective decoherence also prompts information about the correlation length of the environment. In a one dimensional configuration one can change even stronger the qualitative behaviour of the dephasing just by tuning the interaction of the bath.

Species-selective confinement of atoms dressed with multiple radiofrequencies

“…In the absence of tunneling, insights can be made into Markovianity [14][15][16][17] or the chaotic behaviour of a reservoir coupled to two separate quantum systems (here, the two wells) [62].…”

“…Conversely, with tunneling between the wells, demonstrations of non-destructive thermometry and probing of excitations [18], of many-particle correlations [19], and collective decoherence [14] are possible.…”

Probing the degree of non-Markovianity for independent and common environments

“…The third model considered in this work deals with two atoms interacting with an ultracold bosonic rubidium gas in a Bose-Einstein condensate (BEC) state [13,14]. Here, the qubit is represented by an impurity atom in a double-well potential of an optical superlattice of wavelength λ, where the size of the qubit is the distance between the lattice sites, L = λ/4.…”

Robust non-Markovianity in ultracold gases

“…The spatial separation between the two wells is L. For a detailed derivation of the decoherence factor, see [10,11].…”

“…Both cases realize the independent-boson Hamiltonian with an Ohmic-like spectrum of the reservoir [9]. Another proposal in this direction was presented in [10], where an impurity atom in a double-well potential is immersed in a BEC reservoir, forming a spin-boson model with a reservoir spectral function that can be tuned from sub-Ohmic to Ohmic to super-Ohmic. With a super-Ohmic spectrum the spin-boson model can acquire non-Markovian properties [11], thus simulating a prototype of a non-Markovian open quantum system model.…”