70 research outputs found
Diagrammatic Monte Carlo approach to angular momentum in quantum many-particle systems
We introduce a Diagrammatic Monte Carlo (DiagMC) approach to angular momentum
properties of quantum many-particle systems possessing a macroscopic number of
degrees of freedom. The treatment is based on a diagrammatic expansion that
merges the usual Feynman diagrams with the angular momentum diagrams known from
atomic and nuclear structure theory, thereby incorporating the non-Abelian
algebra inherent to quantum rotations. Our approach is applicable at arbitrary
coupling, is free of systematic errors and of finite size effects, and
naturally provides access to the impurity Green function. We exemplify the
technique by obtaining an all-coupling solution of the angulon model, however,
the method is quite general and can be applied to a broad variety of systems in
which particles exchange quantum angular momentum with their many-body
environment.Comment: 6+5 pages, 2+2 figures, accepted for publication in Phys. Rev. Let
Three-body rf association of Efimov trimers
We present a theoretical analysis of rf association of Efimov trimers in a
2-component Bose gas with short-range interactions. Using the adiabatic
hyperspherical Green's function formalism to solve the quantum 3-body problem,
we obtain universal expressions for 3-body rf association rates as a function
of the s-wave scattering length . We find that the association rates scale
as in the limit of large , and diverge as whenever
an Efimov state crosses the atom-dimer threshold (where stands for the
atom-dimer scattering length). Our calculations show that trimer formation
rates as large as cm/s can be achieved with rf Rabi
frequencies of order 1 MHz, suggesting that direct rf association is a powerful
tool of making and probing few-body quantum states in ultracold atomic gases.Comment: 4 pages, 2 figure
Sympathetic cooling of polyatomic molecules with S-state atoms in a magnetic trap
We present a rigorous theoretical study of low-temperature collisions of
polyatomic molecular radicals with ^1S_0 atoms in the presence of an external
magnetic field. Accurate quantum scattering calculations based on ab initio and
scaled interaction potentials show that collision-induced spin relaxation of
the prototypical organic molecule CH_2(X^3B_1) (methylene) and nine other
triatomic radicals in cold 3He gas occurs at a slow rate, demonstrating that
cryogenic buffer-gas cooling and magnetic trapping of these molecules is
feasible with current technology. Our calculations further suggest that it may
be possible to create ultracold gases of polyatomic molecules by sympathetic
cooling with alkaline-earth atoms in a magnetic trap.Comment: 5 pages, 3 figures, 1 tabl
A fundamental limit to the efficiency of spin-exchange optical pumping of 3He nuclei
We establish the existence of a fundamental limit to the efficiency of
spin-exchange optical pumping of 3He nuclei by collisions with spin-polarized
alkali-metal atoms. Using accurate ab initio calculations of molecular
interactions and scattering properties, we show that the maximum 3He spin
polarization that can be achieved in spin-exchange collisions with potassium
(39K) and silver (107Ag) atoms is limited by the anisotropic hyperfine
interaction. We find that spin exchange in Ag-He collisions occurs much faster
than in K-He collisions, suggesting the possibility of using Ag in
spin-exchange optical pumping experiments to increase the production rate of
hyperpolarized 3He. Our analysis indicates that measurements of trap loss rates
of 2S atoms in the presence of cold 3He gas may be used to probe anisotropic
spin-exchange interactions in atom-He collisions.Comment: 5 pages, 4 figure
Feshbach resonances in ultracold 85Rb-87Rb and 6Li-87Rb mixtures
We present an analysis of experimentally accessible magnetic Feshbach
resonances in ultra-cold hetero-nuclear 85Rb-87Rb and 6Li-87Rb mixtures. Using
recent experimental measurements of the triplet scattering lengths for 6Li-87Rb
and 7Li-87Rb mixtures and Feshbach resonances for one combination of atomic
states, we create model potential curves and fine tune them to reproduce the
measured resonances and to predict the location of several experimentally
relevant resonances in Li-Rb collisions. To model 85Rb-87Rb collisions, we use
accurate Rb_2 potentials obtained previously from the analysis of experiments
on 87Rb-87Rb collisions. We find resonances that occur at very low magnetic
fields, below 10 G, which may be useful for entanglement generation in optical
lattices or atom chip magnetic traps.Comment: 8 pages, 5 figure
General classification of qubit encodings in ultracold diatomic molecules
Owing to their rich internal structure and significant long-range
interactions, ultracold molecules have been widely explored as carriers of
quantum information. Several different schemes for encoding qubits into
molecular states, both bare and field-dressed, have been proposed. At the same
time, the rich internal structure of molecules leaves many unexplored
possibilities for qubit encodings. We show that all molecular qubit encodings
can be classified into four classes by the type of the effective interaction
between the qubits. In the case of polar molecules, the four classes are
determined by the relative magnitudes of matrix elements of the dipole moment
operator in the single molecule basis. We exemplify our classification scheme
by considering a new type of encoding of the effective spin-1/2 system into
non-adjacent rotational states (e.g., and ) of polar and non-polar
molecules with the same nuclear spin projection. Our classification scheme is
designed to inform the optimal choice of molecular qubit encoding for quantum
information storage and processing applications, as well as for dynamical
generation of many-body entangled states and for quantum annealing.Comment: 26 pages, 6 figure
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