Diagrammatic Monte Carlo Approach to Angular Momentum in Quantum Many-Particle Systems

Bighin, Giacomo; Tscherbul, Timur V.; Lemeshko, Mikhail

doi:10.1103/physrevlett.121.165301

Cited by 18 publications

(9 citation statements)

References 72 publications

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“…A similar ansatz has been previously shown to provide a good approximation to the energies of polarons 42 and angulons 43 , even far beyond the weak-coupling regime considered in this paper. In Eq.…”

Section: The Microscopic Modelsupporting

confidence: 53%

Quantum many-body dynamics of the Einstein–de Haas effect

Mentink¹,

Katsnelson²,

Lemeshko

2019

Phys. Rev. B

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In 1915, Einstein and de Haas and Barnett demonstrated that changing the magnetization of a magnetic material results in mechanical rotation, and vice versa. At the microscopic level, this effect governs the transfer between electron spin and orbital angular momentum, and lattice degrees of freedom, understanding which is key for molecular magnets, nano-magneto-mechanics, spintronics, and ultrafast magnetism. Until now, the timescales of electron-to-lattice angular momentum transfer remain unclear, since modeling this process on a microscopic level requires addition of an infinite amount of quantum angular momenta. We show that this problem can be solved by reformulating it in terms of the recently discovered angulon quasiparticles, which results in a rotationally invariant quantum many-body theory. In particular, we demonstrate that non-perturbative effects take place even if the electron-phonon coupling is weak and give rise to angular momentum transfer on femtosecond timescales. J λl − ω k ω + iε + ∆E JM J λl − ω k (C9) K2 M J λl (ω) = k |U λ (k) Q λl | 2 ∆E JM 0 J λl − ω k 2 ω + iε + ∆E JM J λl − ω k (C10) with ∆E JM J = E − E JM J and ∆E JM J λl = E − E JM J λl , where E is the variational ground-state energy. The integrals are computed numerically with ε 1 until convergence is achieved. Explicit expressions for the energy of the bare impurity, E JM J , and the energy of the bare impurity with phonons excited, E JM J λl , as well as for Q λl , are given in Appendix B.

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Section: The Microscopic Modelsupporting

confidence: 53%

Quantum many-body dynamics of the Einstein–de Haas effect

Mentink¹,

Katsnelson²,

Lemeshko

2019

Phys. Rev. B

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“…In contrast eq. (25) shows that the typical transition rates for a rotating molecule are bigger by a factor ξ/r 0 . This may raise concerns if angulons can be observed at all.…”

Section: A Single-phonon Rates and Angulon Stabilitymentioning

confidence: 97%

“…Recently the concept of a polaron was extended to impurities with a more complex structure such as a molecule. It was shown that the coupling of rotation to collective excitations of a surrounding BEC can give rise to a new type of quasi-particles termed angulons [21][22][23][24][25]. In the present paper we discuss the cooling dynamics of the rotational degrees of freedom of a single, diatomic molecule immersed in a three-dimensional (3D) Bose-Einstein condensate, see Fig.…”

Section: Introductionmentioning

confidence: 98%

Rotational cooling of molecules in a Bose-Einstein condensate

2019

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We discuss the rotational cooling of diatomic molecules in a Bose-Einstein condensate (BEC) of ultra-cold atoms by emission of phonons with orbital angular momentum. Despite the superfluidity of the BEC there is no frictionless rotation for typical molecules since the dominant cooling occurs via emission of particle-like phonons. Only for macro-dimers, whose size becomes comparable or larger than the condensate healing length, a Landau-like, critical angular momentum exists below which phonon emission is suppressed. We find that the rotational relaxation of typical molecules is in general faster than the cooling of the linear motion of impurities in a BEC. This also leads to a finite lifetime of angulons, quasi-particles of rotating molecules coupled to phonons with orbital angularmomentum. We analyze the dynamics of rotational cooling for homo-nuclear diatomic molecules based on a quantum Boltzmann equation including single-and two-phonon scattering and discuss the effect of thermal phonons.

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“…(2). They involve perturbations on the top of a microscopic deformation of the helium bath, i. e. an infinite number of bosonic excitations [25][26][27] . In the course of the paper, however, we aim to demonstrate that the solutions including up to triple excitations are able to catch changes in molecular spectra for broad range of species measured in helium.…”

Section: A the Angulon Hamiltonianmentioning

confidence: 99%

A simple model for high rotational excitations of molecules in a superfluid

Cherepanov¹,

Bighin²,

Schouder³

et al. 2022

Preprint

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We present a simple quantum mechanical model describing excited rotational states of molecules in superfluid helium nanodroplets, as recently studied in non-adiabatic molecular alignment experiments [Cherepanov et al., Phys. Rev. A 104, L061303 (2021)]. We show that a linear molecule immersed in a superfluid can be seen as an effective symmetric top, similar to the rotational structure of radicals, such as OH or NO, but with the angular momentum of the superfluid playing the role of the electronic angular momentum in free molecules. The model allows to evaluate the effective rotational and centrifugal distortion constants for a broad range of species and to explain the crossover between light and heavy molecules in superfluid 4 He in terms of the many-body wavefunction structure. Most important, the simple theory allows to answer the question as to what happens when the rotational angular momentum of the molecule increases beyond the lowest excited states accessible by infrared spectroscopy. Some of the above mentioned insights can be acquired by analyzing a simple 2 × 2 matrix.

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Diagrammatic Monte Carlo Approach to Angular Momentum in Quantum Many-Particle Systems

Cited by 18 publications

References 72 publications

Quantum many-body dynamics of the Einstein–de Haas effect

Quantum many-body dynamics of the Einstein–de Haas effect

Rotational cooling of molecules in a Bose-Einstein condensate

A simple model for high rotational excitations of molecules in a superfluid

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