Magneto-optical Feshbach resonance: controlling cold collision with quantum interference

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We show theoretically that it is possible to create and manipulate a pair of bound states in continuum in ultracold atoms by two lasers in the presence of a magnetically tunable Feshbach resonance. These bound states are formed due to coherent superposition of two electronically excited molecular bound states and a quasi-bound state in ground-state potential. These superposition states are decoupled from the continuum of two-atom collisional states. Hence, in the absence of other damping processes they are non-decaying.We analyze in detail the physical conditions that can lead to the formation of such states in cold collisions between atoms, and discuss the possible experimental signatures of such states. An extremely narrow and asymmetric shape with a distinct minimum of photoassociative absorption spectrum or scattering cross section as a function of collision energy will indicate the occurrence of a bound state in continuum (BIC).We prove that the minimum will occur at an energy at which the BIC is formed. We discuss how a BIC will be useful for efficient creation of Feshbach molecules and manipulation of cold collisions. Experimental realizations of BIC will pave the way for a new kind of bound-bound spectroscopy in ultracold atoms.

Section: Discussionmentioning

confidence: 99%

Creation and manipulation of bound states in the continuum with lasers: Applications to cold atoms and molecules

Deb

Agarwal

2014

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“…In this context, an ultracold atom-molecule coupled system is very appealing for studying the Fano effect, since the underlying atomic and molecular states are amenable to coherent control. The Fano effect in the photoassociation (PA) of cold atoms in the presence of a magnetic Feshbach resonance has been theoretically predicted previously 26,27 . This effect has been shown to be useful for the creation of a bound state in a continuum 28 and may thereby find important applications in the coherent manipulation of atommolecule coupled systems.…”

Section: Introductionmentioning

confidence: 94%

Fano effect in an ultracold atom-molecule coupled system

Gao

et al. 2019

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The Fano effect or Fano resonance with a characteristically asymmetric line shape originates from quantum interference between direct and indirect transition pathways in continuumbound coupled systems, and is a ubiquitous phenomenon in atomic 1,2 , molecular 3 , nuclear 4,5 and solid-state physics 6-8 . In optical nanoscale structures, the Fano effect has wide-ranging applications that include optical filtering 9 , sensing 10 , all-optical switching 11 , quantum interferometry 12 and nonlinear optics 13 , and this opens new avenues for photonic devices. The emergent area of ultracold atomic and molecular gases presents an ideal platform for studying Fano resonances, since the physical parameters of these gases can be extensively tuned with high precision using external fields. However, an experimental demonstration of the Fano effect in hybridized atom-molecular coupled systems has remained elusive. Here, we report on observations of the Fano effect in molecular spectra obtained by photoassociation (PA) near a d-wave Feshbach resonance. This effect occurs due to quantum interference in PA transitions involving the continuum of atom-atom scattering states, the underlying Feshbach and photoassociated excited bound molecular states. We measure the variation in atom loss rate with an external magnetic field close to the Feshbach resonance in the presence of PA laser, and thereby clearly demonstrate the Fano effect. Our results further reveal that the Fano effect has significant influence on spectral shifts. Based on Fano's method, we develop a theory that explains the observed experimental results relatively well. Our theoretical formulation takes into account quantum interference between or among multiple transition pathways and between inelastic channels. Our results present a novel method for tuning the collisional interaction strength with laser light using Fano resonance.

“…The operatorŜ † E = |φ n b E | is a raising operator. H c is exactly diagonalizable [22,23] in the spirit of Fano's theory [3]. The eigenstate of H c is the dressed continuum expressed as…”

Section: Ve(r)mentioning

confidence: 99%

“…The manipulation of VIC with PA may be important for controlling decoherence and dissipation in cold molecules. It may also be used for coherent control of atom-molecule conversion and optical [29,30] and magneto-optical Feshbach resonance [23].…”

Section: Ve(r)mentioning

confidence: 99%

Vacuum-induced coherence in ultracold photoassociative rovibrational excitations

Das¹,

Rakshit²,

Deb³

2012

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We show that coherence between two excited rovibrational states belonging to the same molecular electronic configuration arises quite naturally due to their interaction with electromagnetic vacuum. For initial preparation of a molecule in the desired rovibrational states, we propose to employ the method of ultracold photoassociation. Spontaneous decay of the excited molecule then gives rise to vacuum-induced coherence between the excited ro-vibrational states. We demonstrate theoretically an interesting interplay of effects due to vacuum-induced coherence and photoassociation. We apply our theory to photoassociation of bosonic ytterbium ( 174 Yb) atoms, which appear to be a promising system for exploring such interplay. The effects discussed here can be important for controlling decoherence and dissipation in molecular systems.