Enhancement of spin coherence in a spin-1 Bose-Einstein condensate by dynamical decoupling approaches

Abstract

We study the enhancement of spin coherence with periodic, concatenated, or Uhrig dynamical decoupling N -pulse sequences in a spin-1 Bose condensate, where the intrinsic dynamical instability in such a ferromagnetically interacting condensate causes spin decoherence and eventually leads to a multiple spatial-domain structure or a spin texture. Our results show that all the three sequences successfully enhance the spin coherence by pushing the wave vector of the most unstable mode in the condensate to a larger value. Among the three sequences with the same number of pulses, the concatenated one shows the best performance in preserving the spin coherence. More interestingly, we find that all the three sequences exactly follow the same enhancement law, k−T 1/2 = c, with k− the wave vector of the most unstable mode, T the sequence period, and c a sequence-dependent constant. Such a law between k− and T is also derived analytically for an attractive scalar Bose condensate subjecting to a periodic dynamical decoupling sequence.

Control of spin current in a Bose gas by periodic application ofπpulses

“…Dynamical decoupling techniques such as quantum bang-bang control [7], in which undesired environmental interactions are averaged out by repeated application of suitable pulses, provides one powerful solution for this purpose. By application of dynamical decoupling, it has been theoretically shown that spin coherence can be prolonged in a spin-1 Bose gas [8]. Furthermore, the effects of weak magnetic dipole-dipole interactions (MDDIs) have been revealed [9] and controlled using dynamical decoupling techniques [10].…”

Coherent zero-field magnetization resonance in a dipolar spin-1 Bose-Einstein condensate

“…However, the resonant dipolar magnetization dynamics can be revealed under current experimental conditions if we employ dynamical decoupling techniques to cancel the Zeeman effect [1,28,32]. In particular, by applying frequent π x pulse, which rotates the condensate spin 180 o along x-axis, the Zeeman effect is eliminated while leaving the dipolar interaction intact to the leading order.…”

“…Recently, with the precision measurement of an ultraweak or zero magnetic field, the investigation of the nonsecular dipolar interaction effects becomes revived in the areas of zero-field nuclear magnetic resonance and dipolar spinor Bose-Einstein condensates [7][8][9][10][11]. Particularly, the achievements in spinor Bose-Einstein condensates (BECs) provide a highly tunable and controllable system where the spin interactions, including the magnetic dipolar interaction, can be accurately engineered [3,[12][13][14][15][16][17][18][19]. Such dipolar spinor condensates make them an ideal testbed to extensively explore the full magnetic dipolar interaction effect, including not only the secular part but also the nonsecular one which breaks the rotational symmetry and definitely brings new physics.…”

Manipulating dipolar and spin-exchange interactions in spin-1 Bose-Einstein condensates

“…Accordingly, it is highly desired to suppress one spin interaction and make the other dominant. Although efforts have been made to prohibit either the dipolar interaction [21] or the spin exchange interaction [23,24], it is yet difficult to clearly separate the individual effects.…”

“…In this paper, we propose to independently suppress the dipolar and the spin-exchange interaction by a sequence of rf pulses ( Fig. 1) and optical Feshbach periodic dynamical decoupling (PDD) sequences [24], respectively. This scheme was verified by the analytic derivations, demonstrating that the manipulations of the relative strength between the two spin interactions enable experimentalists to unambiguously distinguish the specific role of the dipolar and the spin-exchange interactions.…”