arXiv subjects

Jeremy M. Hutson

Publications and source records attributed to Jeremy M. Hutson.

At least 55 records · Page 3Linked to original sources

arXiv2020

Coherent optical creation of a single molecule

We report coherent association of atoms into a single weakly bound NaCs molecule in an optical tweezer through an optical Raman transition. The Raman technique uses a deeply bound electronic excited intermediate state to achieve a large transition dipole moment while reducing photon scattering. Starting from two atoms in their relative motional ground state, we achieve an optical transfer efficiency of 69%. The molecules have a binding energy of 770.2MHz at 8.83(2)G. This technique does not rely on Feshbach resonances or narrow excited-state lines and may allow a wide range of molecular species to be assembled atom-by-atom.

physics.atom-ph↗

arXiv2020

Observation of Efimov Universality across a Non-Universal Feshbach Resonance in \textsuperscript{39}K

We study three-atom inelastic scattering in ultracold \textsuperscript{39}K near a Feshbach resonance of intermediate coupling strength. The non-universal character of such resonance leads to an abnormally large Efimov absolute length scale and a relatively small effective range $r_e$, allowing the features of the \textsuperscript{39}K Efimov spectrum to be better isolated from the short-range physics. Meticulous characterization of and correction for finite temperature effects ensure high accuracy on the measurements of these features at large-magnitude scattering lengths. For a single Feshbach resonance, we unambiguously locate four distinct features in the Efimov structure. Three of these features form ratios that obey the Efimov universal scaling to within 10\%, while the fourth feature, occurring at a value of scattering length closest to $r_e$, instead deviates from the universal value.

cond-mat.quant-gas↗

arXiv2020

Prospects of forming high-spin polar molecules from ultracold atoms

We have investigated Feshbach resonances in collisions of high-spin atoms such as Er and Dy with closed-shell atoms such as Sr and Yb, using coupled-channel scattering and bound-state calculations. We consider both low-anisotropy and high-anisotropy limits. In both regimes we find many resonances with a wide variety of widths. The wider resonances are suitable for tuning interatomic interactions, while some of the narrower resonances are highly suitable for magnetoassociation to form high-spin molecules. These molecules might be transferred to short-range states, where they would have large magnetic moments and electric dipole moments that can be induced with very low electric fields. The results offer the opportunity to study mixed quantum gases where one species is dipolar and the other is not, and open up important prospects for a new field of ultracold high-spin polar molecules.

physics.atom-ph↗

arXiv2020

Sticky collisions of ultracold RbCs molecules

Understanding and controlling collisions is crucial to the burgeoning field of ultracold molecules. All experiments so far have observed fast loss of molecules from the trap. However, the dominant mechanism for collisional loss is not well understood when there are no allowed 2-body loss processes. Here we experimentally investigate collisional losses of nonreactive ultracold RbCs molecules, and compare our findings with the sticky collision hypothesis that pairs of molecules form long-lived collision complexes. We demonstrate that loss of molecules occupying their rotational and hyperfine ground state is best described by second-order rate equations, consistent with the expectation for complex-mediated collisions, but that the rate is lower than the limit of universal loss. The loss is insensitive to magnetic field but increases for excited rotational states. We demonstrate that dipolar effects lead to significantly faster loss for an incoherent mixture of rotational states.

cond-mat.quant-gas↗

arXiv2020

Microwave coherent control of ultracold ground-state molecules formed by short-range photoassociation

We report the observation of microwave coherent control of rotational states of ultracold $^{85}$Rb$^{133}$Cs molecules formed in their vibronic ground state by short-range photoassociation. Molecules are formed in the single rotational state $X(v=0,J=1)$ by exciting pairs of atoms to the short-range state $(2)^{3}Π_{0^{-}} (v=11, J=0)$, followed by spontaneous decay. We use depletion spectroscopy to record the dynamic evolution of the population distribution and observe clear Rabi oscillations while irradiating on a microwave transition between coupled neighbouring rotational levels. A density-matrix formalism that accounts for longitudinal and transverse decay times reproduces both the dynamic evolution during the coherent process and the equilibrium population. The coherent control reported here is valuable both for investigating coherent quantum effects and for applications of cold polar molecules produced by continuous short-range photoassociation.

physics.atom-ph↗

arXiv2020

Controlling the ac Stark effect of RbCs with dc electric and magnetic fields

We investigate the effects of static electric and magnetic fields on the differential ac Stark shifts for microwave transitions in ultracold bosonic $^{87}$Rb$^{133}$Cs molecules, for light of wavelength $λ= 1064~\mathrm{nm}$. Near this wavelength we observe unexpected two-photon transitions that may cause trap loss. We measure the ac Stark effect in external magnetic and electric fields, using microwave spectroscopy of the first rotational transition. We quantify the isotropic and anisotropic parts of the molecular polarizability at this wavelength. We demonstrate that a modest electric field can decouple the nuclear spins from the rotational angular momentum, greatly simplifying the ac Stark effect. We use this simplification to control the ac Stark shift using the polarization angle of the trapping laser.

physics.atom-ph↗

arXiv2020

Forming a single molecule by magnetoassociation in an optical tweezer

We demonstrate the formation of a single NaCs molecule in an optical tweezer by magnetoassociation through an s-wave Feshbach resonance at 864.11(5)G. Starting from single atoms cooled to their motional ground states, we achieve conversion efficiencies of 47(1)%, and measure a molecular lifetime of 4.7(7)ms. By construction, the single molecules are predominantly (77(5)%) in the center-of-mass motional ground state of the tweezer. Furthermore, we produce a single p-wave molecule near 807G by first preparing one of the atoms with one quantum of motional excitation. Our creation of a single weakly bound molecule in a designated internal state in the motional ground state of an optical tweezer is a crucial step towards coherent control of single molecules in optical tweezer arrays.

physics.atom-ph↗

arXiv2020

A robust entangling gate for polar molecules using magnetic and microwave fields

Polar molecules are an emerging platform for quantum technologies based on their long-range electric dipole-dipole interactions, which open new possibilities for quantum information processing and the quantum simulation of strongly correlated systems. Here, we use magnetic and microwave fields to design a fast entangling gate with $>0.999$ fidelity and which is robust with respect to fluctuations in the trapping and control fields and to small thermal excitations. These results establish the feasibility to build a scalable quantum processor with a broad range of molecular species in optical-lattice and optical-tweezers setups.

quant-ph↗

arXiv2020

Characterizing quasibound states and scattering resonances

Characterizing quasibound states from coupled-channel scattering calculations can be a laborious task, involving extensive manual iteration and fitting. We present an automated procedure, based on the phase shift or S-matrix eigenphase sum, that reliably converges on a quasibound state (or scattering resonance) from some distance away. It may be used for both single-channel and multichannel scattering. It produces the energy and width of the state and the phase shift of the background scattering, and hence the lifetime of the state. It also allows extraction of partial widths for decay to individual open channels. We demonstrate the method on a very narrow state in the Van der Waals complex Ar--H$_2$, which decays only by vibrational predissociation, and on near-threshold states of $^{85}$Rb$_2$, whose lifetime varies over 4 orders of magnitude as a function of magnetic field.

physics.atom-ph↗

arXiv2020

Long rotational coherence times of molecules in a magnetic trap

Polar molecules in superpositions of rotational states exhibit long-range dipolar interactions, but maintaining their coherence in a trapped sample is a challenge. We present calculations that show many laser-coolable molecules have convenient rotational transitions that are exceptionally insensitive to magnetic fields. We verify this experimentally for CaF where we find a transition with sensitivity below 5 Hz G$^{-1}$ and use it to demonstrate a rotational coherence time of 6.4(8) ms in a magnetic trap. Simulations suggest it is feasible to extend this to more than 1 s using a smaller cloud in a biased magnetic trap.

physics.atom-ph↗

arXiv2019

Inelastic collisions in radiofrequency-dressed mixtures of ultracold atoms

Radiofrequency (RF)-dressed potentials are a promising technique for manipulating atomic mixtures, but so far little work has been undertaken to understand the collisions of atoms held within these traps. In this work, we dress a mixture of 85Rb and 87Rb with RF radiation, characterize the inelastic loss that occurs, and demonstrate species-selective manipulations. Our measurements show the loss is caused by two-body 87Rb+85Rb collisions, and we show the inelastic rate coefficient varies with detuning from the RF resonance. We explain our observations using quantum scattering calculations, which give reasonable agreement with the measurements. The calculations consider magnetic fields both perpendicular to the plane of RF polarization and tilted with respect to it. Our findings have important consequences for future experiments that dress mixtures with RF fields.

cond-mat.quant-gas↗

arXiv2019

Microwave shielding of ultracold polar molecules with imperfectly circular polarization

We investigate the use of microwave radiation to produce a repulsive shield between pairs of ultracold polar molecules and prevent collisional losses that occur when molecular pairs reach short range. We carry out coupled-channels calculations on RbCs+RbCs and CaF+CaF collisions in microwave fields. We show that effective shielding requires predominantly circular polarization, but can still be achieved with elliptical polarization that is around 90% circular.

physics.atom-ph↗

arXiv2019

Ultracold collisions in the Yb-Li mixture system

We report our experimental results on the collisional physics between non-S-state atoms (ytterbium (Yb), effectively a two-electron system, in the metastable ${}^3\mathrm{P}_2$ state) and S-state atoms (lithium (Li), an alkali metal, in the ground state). At low magnetic fields, by measuring inelastic interspecies collisional losses in the double quantum degenerate mixture we reveal the strong dependence of the inelastic losses on the internal spin states of both species and suppressed losses in stretched state configurations. Increasing the magnetic field up to 800 G we further investigate the magnetic field dependence of the collisional interactions. There, smoothly increasing inelastic losses are observed towards higher fields. The combined knowledge of both the magnetic field and the spin state dependence of the collisional losses of this prototypical mixture system of non-S-state and S-state atoms provides a significant step forward towards controllable impurity physics realized in the Yb-Li ultracold system.

cond-mat.quant-gas↗

arXiv2019

Time delays in ultracold atomic and molecular collisions

We study the behavior of the Eisenbud-Wigner collisional time delay around Feshbach resonances in cold and ultracold atomic and molecular collisions. We carry out coupled-channels scattering calculations on ultracold Rb and Cs collisions. In the low-energy limit, the time delay is proportional to the scattering length, so exhibits a pole as a function of applied field. At high energy, it exhibits a Lorentzian peak as a function of either energy or field. For narrow resonances, the crossover between these two regimes occurs at an energy proportional to the square of the resonance strength parameter $s_\textrm{res}$. For wider resonances, the behavior is more complicated and we present an analysis in terms of multichannel quantum defect theory.

physics.atom-ph↗

arXiv2019

Magnetic Feshbach resonances in ultracold collisions between Cs and Yb atoms

We investigate magnetically tunable Feshbach resonances in ultracold collisions between ground-state Yb and Cs atoms, using coupled-channel calculations based on an interaction potential recently determined from photoassociation spectroscopy. We predict resonance positions and widths for all stable isotopes of Yb, together with resonance decay parameters where appropriate. The resonance patterns are richer and more complicated for fermionic Yb than for spin-zero isotopes, because there are additional level splittings and couplings due to scalar and tensorial Yb hyperfine interactions. We examine collisions involving Cs atoms in a variety of hyperfine states, and identify resonances that appear most promising for experimental observation and for magnetoassociation to form ultracold CsYb molecules.

physics.atom-ph↗

arXiv2019

Ultracold collisions of Cs in excited hyperfine and Zeeman states

We investigate Cs+Cs scattering in excited Zeeman and hyperfine states. We calculate the real and imaginary parts of the s-wave scattering length; the imaginary part directly provides the rate coefficient for 2-body inelastic loss, while the real part allows us to identify regions of magnetic field where 3-body recombination will be slow. We identify field regions where Cs in its $(f,m_f)=(3,+2)$ and $(3,+1)$ states may be stable enough to allow Bose-Einstein condensation, and additional regions for these and the $(3,0)$ and $(3,-3)$ states where high-density clouds should be long-lived.

physics.atom-ph↗

arXiv2019

MOLSCAT: a program for non-reactive quantum scattering calculations on atomic and molecular collisions

MOLSCAT is a general-purpose program for quantum-mechanical calculations on nonreactive atom-atom, atom-molecule and molecule-molecule collisions. It constructs the coupled-channel equations of atomic and molecular scattering theory, and solves them by propagating the wavefunction or log-derivative matrix outwards from short range to the asymptotic region. It then applies scattering boundary conditions to extract the scattering matrix (S matrix). Built-in coupling cases include atom + rigid linear molecule, atom + vibrating diatom, atom + rigid symmetric top, atom + asymmetric or spherical top, rigid diatom + rigid diatom, rigid diatom + asymmetric top, and diffractive scattering of an atom from a crystal surface. Interaction potentials may be specified either in program input (for simple cases) or with user-supplied routines. For the built-in coupling cases, MOLSCAT can loop over partial wave (or total angular momentum) to calculate elastic and inelastic cross integral sections and spectroscopic line-shape cross sections. Post-processors are available to calculate differential cross sections, transport, relaxation and Senftleben-Beenakker cross sections, and to fit the parameters of scattering resonances. MOLSCAT also provides an interface for plug-in routines to specify coupling cases (Hamiltonians and basis sets) that are not built in; plug-in routines are supplied to handle collisions of a pair of alkali-metal atoms with hyperfine structure in an applied magnetic field. For low-energy scattering, MOLSCAT can calculate scattering lengths and effective ranges and can locate and characterize scattering resonances as a function of an external variable such as the magnetic field.

physics.chem-ph↗

arXiv2019

BOUND and FIELD: programs for calculating bound states of interacting pairs of atoms and molecules

The BOUND program calculates the bound states of a complex formed from two interacting particles using coupled-channel methods. It is particularly suitable for the bound states of atom-molecule and molecule-molecule Van der Waals complexes and for the near-threshold bound states that are important in ultracold physics. It uses a basis set for all degrees of freedom except $R$, the separation of the centres of mass of the two particles. The Schrödinger equation is expressed as a set of coupled equations in $R$. Solutions of the coupled equations are propagated outwards from the classically forbidden region at short range and inwards from the classically forbidden region at long range, and matched at a point in the central region. Built-in coupling cases include atom + rigid linear molecule, atom + vibrating diatom, atom + rigid symmetric top, atom + asymmetric or spherical top, rigid diatom + rigid diatom, and rigid diatom + asymmetric top. Both programs provide an interface for plug-in routines to specify coupling cases (Hamiltonians and basis sets) that are not built in. With appropriate plug-in routines, BOUND can take account of the effects of external electric, magnetic and electromagnetic fields, locating bound-state energies at fixed values of the fields. The related program FIELD uses the same plug-in routines and locates values of the fields where bound states exist at a specified energy. As a special case, it can locate values of the external field where bound states cross scattering thresholds and produce zero-energy Feshbach resonances. Plug-in routines are supplied to handle the bound states of a pair of alkali-metal atoms with hyperfine structure in an applied magnetic field.

physics.chem-ph↗