arXiv subjects

B. Naylor

Publications and source records attributed to B. Naylor.

7 recordsLinked to original sources

arXiv2018

Exploring out-of-equilibrium quantum magnetism and thermalization in a spin-3 many-body dipolar lattice system

Understanding quantum thermalization through entanglement build-up in isolated quantum systems addresses fundamental questions on how unitary dynamics connects to statistical physics. Here, we study the spin dynamics and approach towards local thermal equilibrium of a macroscopic ensemble of S = 3 spins prepared in a pure coherent spin state, tilted compared to the magnetic field, under the effect of magnetic dipole-dipole interactions. The experiment uses a unit filled array of 104 chromium atoms in a three dimensional optical lattice, realizing the spin-3 XXZ Heisenberg model. The buildup of quantum correlation during the dynamics, especially as the angle approaches pi/2, is supported by comparison with an improved numerical quantum phase-space method and further confirmed by the observation that our isolated system thermalizes under its own dynamics, reaching a steady state consistent with the one extracted from a thermal ensemble with a temperature dictated from the system's energy. This indicates a scenario of quantum thermalization which is tied to the growth of entanglement entropy. Although direct experimental measurements of the Renyi entropy in our macroscopic system are unfeasible, the excellent agreement with the theory, which can compute this entropy, does indicate entanglement build-up.

cond-mat.quant-gas↗

arXiv2017

Bright soliton to quantum droplet transition in a mixture of Bose-Einstein condensates

Attractive Bose-Einstein condensates can host two types of macroscopic self-bound states of different nature: bright solitons and quantum liquid droplets. Here, we investigate the connection between them with a Bose-Bose mixture confined in an optical waveguide. We develop a simple theoretical model to show that, depending on atom number and interaction strength, solitons and droplets can be smoothly connected or remain distinct states coexisting only in a bi-stable region. We experimentally measure their spin composition, extract their density for a broad range of parameters and map out the boundary of the region separating solitons from droplets.

cond-mat.quant-gas↗

arXiv2017

Quantum liquid droplets in a mixture of Bose-Einstein condensates

Quantum droplets are small clusters of atoms self-bound by the balance of attractive and repulsive forces. Here we report on the observation of a novel type of droplets, solely stabilized by contact interactions in a mixture of two Bose-Einstein condensates. We demonstrate that they are several orders of magnitude more dilute than liquid helium by directly measuring their size and density via in situ imaging. Moreover, by comparison to a single-component condensate, we show that quantum many-body effects stabilize them against collapse. We observe that droplets require a minimum atom number to be stable. Below, quantum pressure drives a liquid-to-gas transition that we map out as a function of interaction strength. These ultra-dilute isotropic liquids remain weakly interacting and constitute an ideal platform to benchmark quantum many-body theories.

cond-mat.quant-gas↗

arXiv2017

Spin mixing and protection of ferromagnetism in a spinor dipolar condensate

We study spin mixing dynamics in a chromium dipolar Bose-Einstein Condensate, after tilting the atomic spins by an angle $\theta$ with respect to the magnetic field. Spin mixing is triggered by dipolar coupling, but, once dynamics has started, it is mostly driven by contact interactions. For the particular case $\theta=\pi/2$, an external spin-orbit coupling term induced by a magnetic gradient is required to enable the dynamics. Then the initial ferromagnetic character of the gas is locally preserved, an unexpected feature that we attribute to large spin-dependent contact interactions.

cond-mat.quant-gas↗

arXiv2014

A chromium dipolar Fermi sea

We report on the production of a degenerate Fermi gas of 53Cr atoms, polarized in the state F=9/2, m_F=-9/2, by sympathetic cooling with bosonic S=3, m_S=-3 52Cr atoms. We load in an optical dipole trap 3.10^4 53Cr atoms with 10^6 52Cr atoms. Despite this initial small number of fermionic atoms, we reach a final temperature of T=0.6 T_f (Fermi temperature), with up to 10^3 53Cr atoms. This surprisingly efficient evaporation stems from an inter-isotope scattering length |a_{BF}| = (85+/- 10) a_{Bohr} which is small enough to reduce evaporative losses of the fermionic isotope, but large enough to insure thermalization.

cond-mat.quant-gas↗

arXiv2014

Dipolar atomic spin ensembles in a double-well potential

We experimentally study the spin dynamics of mesoscopic ensembles of ultracold magnetic spin-3 atoms located in two separated wells of an optical dipole trap. We use a radio-frequency sweep to selectively flip the spin of the atoms in one of the wells, which produces two separated spin domains of opposite polarization. We observe that these engineered spin domains are metastable with respect to the long-range magnetic dipolar interactions between the two ensembles. The absence of inter-cloud dipolar spin-exchange processes reveals a classical behavior, in contrast to previous results with atoms loaded in an optical lattice. When we merge the two subsystems, we observe spin-exchange dynamics due to contact interactions which enable the first determination of the s-wave scattering length of 52Cr atoms in the S=0 molecular channel a_0=13.5^{+11}_{-10.5}a_B (where a_B is the Bohr radius).

physics.atom-ph↗

arXiv2013

High Spectral Resolution Measurement of the Sunyaev-Zel'dovich Effect Null with Z-Spec

The Sunyaev-Zel'dovich (SZ) effect spectrum crosses through a null where dT_CMB = 0 near nu_0 = 217 GHz. In a cluster of galaxies, nu_0 can be shifted from the canonical thermal SZ effect value by corrections to the SZ effect scattering due to the properties of the inter-cluster medium. We have measured the SZ effect in the hot galaxy cluster RX J1347.5-1145 with Z-Spec, an R ~ 300 grating spectrometer sensitive between 185 and 305 GHz. These data comprise a high spectral resolution measurement around the null of the SZ effect and clearly exhibit the transition from negative to positive dT_CMB over the Z-Spec band. The SZ null position is measured to be nu_0 = 225.8 \pm 2.5 (stat.) \pm 1.2 (sys.) GHz, which differs from the canonical null frequency by 3.0 sigma and is evidence for modifications to the canonical thermal SZ effect shape. Assuming the measured shift in nu_0 is due only to relativistic corrections to the SZ spectrum, we place the limit T_e = 17.1 \pm 5.3 keV from the zero-point measurement alone. By simulating the response of the instrument to the sky, we are able to generate likelihood functions in {y_0, T_e, v_pec} space. For v_pec = 0 km/s, we measure the best fitting SZ model to be y_0 = 4.6 (+0.6, -0.9) x 10^-4, T_e,0 = 15.2 (+12,-7.4) keV. When v_pec is allowed to vary, a most probable value of v_pec = +450 \pm 810 km/s is found.

astro-ph.CO↗