arXiv subjects

Bo Yan

Publications and source records attributed to Bo Yan.

119 records · Page 7Linked to original sources

arXiv2015

Prospects for a Narrow Line MOT in YO

In addition to being suitable for laser cooling and trapping in a magneto-optical trap (MOT) using a relatively broad ($\sim$5 MHz) transition, the molecule YO possesses a narrow-line transition. This forbidden transition between the $X^{2}Σ$ and $A'^{2}Δ_{3/2}$ states has linewidth $\sim$2$π\times$160 kHz. After cooling in a MOT on the $X^{2}Σ$ to $A^{2}Π_{1/2}$ (orange) transition, the narrow (red) transition can be used to further cool the sample, requiring only minimal additions to the first stage system. The narrow line cooling stage will bring the temperature from $\sim$1 mK to $\sim$10 $μ$K, significantly advancing the frontier on direct cooling achievable for molecules.

physics.atom-ph↗

arXiv2015

Rotational state microwave mixing for laser cooling of complex diatomic molecules

We demonstrate the mixing of rotational states in the ground electronic state using microwave radiation to enhance optical cycling in the molecule yttrium (II) monoxide (YO). This mixing technique is used in conjunction with a frequency modulated and chirped continuous wave laser to slow longitudinally a cryogenic buffer gas beam of YO. We generate a measurable flux of YO below 10~m/s, directly loadable into a three-dimensional magneto-optical trap. This technique opens the door for laser cooling of molecules with more complex structure.

physics.atom-ph↗

arXiv2014

Many-body dynamics of dipolar molecules in an optical lattice

Understanding the many-body dynamics of isolated quantum systems is one of the central challenges in modern physics. To this end, the direct experimental realization of strongly correlated quantum systems allows one to gain insights into the emergence of complex phenomena. Such insights enable the development of theoretical tools that broaden our understanding. Here, we theoretically model and experimentally probe with Ramsey spectroscopy the quantum dynamics of disordered, dipolar-interacting, ultracold molecules in a partially filled optical lattice. We report the capability to control the dipolar interaction strength, and we demonstrate that the many-body dynamics extends well beyond a nearest-neighbor or mean-field picture, and cannot be quantitatively described using previously available theoretical tools. We develop a novel cluster expansion technique and demonstrate that our theoretical method accurately captures the measured dependence of the spin dynamics on molecule number and on the dipolar interaction strength. In the spirit of quantum simulation, this agreement simultaneously benchmarks the new theoretical method and verifies our microscopic understanding of the experiment. Our findings pave the way for numerous applications in quantum information science, metrology, and condensed matter physics.

cond-mat.quant-gas↗

arXiv2013

Suppressing the loss of ultracold molecules via the continuous quantum Zeno effect

We investigate theoretically the suppression of two-body losses when the on-site loss rate is larger than all other energy scales in a lattice. This work quantitatively explains the recently observed suppression of chemical reactions between two rotational states of fermionic KRb molecules confined in one-dimensional tubes with a weak lattice along the tubes [Yan et al., Nature 501, 521-525 (2013)]. New loss rate measurements performed for different lattice parameters but under controlled initial conditions allow us to show that the loss suppression is a consequence of the combined effects of lattice confinement and the continuous quantum Zeno effect. A key finding, relevant for generic strongly reactive systems, is that while a single-band theory can qualitatively describe the data, a quantitative analysis must include multiband effects. Accounting for these effects reduces the inferred molecule filling fraction by a factor of five. A rate equation can describe much of the data, but to properly reproduce the loss dynamics with a fixed filling fraction for all lattice parameters we develop a mean-field model and benchmark it with numerically exact time-dependent density matrix renormalization group calculations.

quant-ph↗

arXiv2013

Realizing a lattice spin model with polar molecules

With the recent production of polar molecules in the quantum regime, long-range dipolar interactions are expected to facilitate the understanding of strongly interacting many-body quantum systems and to realize lattice spin models for exploring quantum magnetism. In atomic systems, where interactions require wave function overlap, effective spin interactions on a lattice can be realized via superexchange; however, the coupling is weak and limited to nearest-neighbor interactions. In contrast, dipolar interactions exist in the absence of tunneling and extend beyond nearest neighbors. This allows coherent spin dynamics to persist even at high entropy and low lattice filling. Effects of dipolar interactions in ultracold molecular gases have so far been limited to the modification of chemical reactions. We now report the observation of dipolar interactions of polar molecules pinned in a 3D optical lattice. We realize a lattice spin model with spin encoded in rotational states, prepared and probed by microwaves. This spin-exchange interaction arises from the resonant exchange of rotational angular momentum between two molecules. We observe clear oscillations in the evolution of the spin coherence in addition to an overall decay. The frequency of these oscillations, the strong dependence of the spin coherence time on the lattice filling, and the effect of a multi-pulse sequence designed to reverse dynamics due to two-body exchange interactions all provide evidence of dipolar interactions. We also demonstrate suppression of loss in weak lattices due to a quantum Zeno mechanism. Measurements of these tunneling-induced losses allow us to independently determine the lattice filling factor. These results comprise an initial exploration of the behavior of many-body spin models with direct, long-range spin interactions and lay the groundwork for future studies of many-body dynamics in spin lattices.

physics.atom-ph↗

arXiv2013

Lattice Boltzmann model for combustion and detonation

In this paper we present a lattice Boltzmann model for combustion and detonation. In this model the fluid behavior is described by a finite-difference lattice Boltzmann model by Gan et al. [Physica A, 2008, 387: 1721]. The chemical reaction is described by the Lee-Tarver model [Phys. Fluids, 1980, 23: 2362]. The reaction heat is naturally coupled with the flow behavior. Due to the separation of time scales in the chemical and thermodynamic processes, a key technique for a successful simulation is to use the operator-splitting scheme. The new model is verified and validated by well-known benchmark tests. As a specific application of the new model, we studied the simple steady detonation phenomenon. To show the merit of LB model over the traditional ones, we focus on the reaction zone to study the non-equilibrium effects. It is interesting to find that, at the von Neumann peak, the system is nearly in its thermodynamic equilibrium. At the two sides of the von Neumann peak, the system deviates from its equilibrium in opposite directions. In the front of von Neumann peak, due to the strong compression from the reaction product behind the von Neumann peak, the system experiences a sudden deviation from thermodynamic equilibrium. Behind the von Neumann peak, the release of chemical energy results in thermal expansion of the matter within the reaction zone, which drives the system to deviate the thermodynamic equilibrium in the opposite direction. From the deviation from thermodynamic equilibrium, defined in this paper, one can understand more on the macroscopic effects of the system due to the deviation from its thermodynamic equilibrium.

cond-mat.soft↗

arXiv2012

Collective Dipole Oscillation of a Spin-Orbit Coupled Bose-Einstein Condensate

We present an experimental study of the collective dipole oscillation of a spin-orbit coupled Bose-Einstein condensate in a harmonic trap. Dynamics of the center-of-mass dipole oscillation is studied in a broad parameter region, as a function of spin-orbit coupling parameters as well as oscillation amplitude. Anharmonic properties beyond effective-mass approximation are revealed, such as amplitude-dependent frequency and finite oscillation frequency at place with divergent effective mass. These anharmonic behaviors agree quantitatively with variational wave-function calculations. Moreover, we experimentally demonstrate a unique feature of spin-orbit coupled system predicted by a sum-rule approach, stating that spin polarization susceptibility--a static physical quantity--can be measured via dynamics of dipole oscillation. The divergence of polarization susceptibility is observed at the quantum phase transition that separates magnetic nonzero-momentum condensate from nonmagnetic zero-momentum phase. The good agreement between the experimental and theoretical results provides a bench mark for recently developed theoretical approaches.

cond-mat.quant-gas↗

arXiv2011

Long-lived dipolar molecules and Feshbach molecules in a 3D optical lattice

We have realized long-lived ground-state polar molecules in a 3D optical lattice, with a lifetime of up to 25 s, which is limited only by off-resonant scattering of the trapping light. Starting from a 2D optical lattice, we observe that the lifetime increases dramatically as a small lattice potential is added along the tube-shaped lattice traps. The 3D optical lattice also dramatically increases the lifetime for weakly bound Feshbach molecules. For a pure gas of Feshbach molecules, we observe a lifetime of >20 s in a 3D optical lattice; this represents a 100-fold improvement over previous results. This lifetime is also limited by off-resonant scattering, the rate of which is related to the size of the Feshbach molecule. Individually trapped Feshbach molecules in the 3D lattice can be converted to pairs of K and Rb atoms and back with nearly 100% efficiency.

physics.atom-ph↗

arXiv2008

Bose-Einstein condensation on an atom chip

We report an experiment of creating Bose-Einstein condensate (BEC) on an atom chip. The chip based Z-wire current and a homogeneous bias magnetic field create a tight magnetic trap, which allows for a fast production of BEC. After an 4.17s forced radio frequency evaporative cooling, a condensate with about 3000 atoms appears. And the transition temperature is about 300nK. This compact system is quite robust, allowing for versatile extensions and further studying of BEC.

physics.atom-ph↗

arXiv2008

Atomic Frequency standards Based on Pulsed Coherent Light Storage

We propose a new scheme of microwave frequency standards based on pulsed coherent optical information storage. Unlike the usual frequency reference where the Ramsey fringe is printed on the population of a certain state, we print the Ramsey fringe on the coherence. Then the coherence is detected in the form of a retrieval light. The central line of the Ramsey fringe can be used as a frequency reference in an absorption-cell-based atomic frequency standard. This scheme is free of light shifts as the interrogating process is separated from the optical pumping processes, and the cavity pulling effect is negligible due to the low Q requirement. Encoding the Ramsey interference into the retrieval light pulse has the merit of high signal to noise ratio and the estimated frequency stability of shot noise limit is about $2\times10^{-14}$ in 1 second, this scheme is promising for building small, compact and stable atomic frequency standards.

physics.atom-ph↗

arXiv2007

A Radio-Frequency Atom Chip for Guiding Neutral Atoms

We propose two kinds of wire configurations fabricated on an atom chip surface for creating two-dimensional (2D) adiabatic rf guide with an inhomogeneous rf magnetic field and a homogenous dc magnetic field. The guiding state can be selected by changing the detuning between the frequency of rf magnetic field and the resonance frequency of two Zeeman sublevels. We also discuss the optimization of loading efficiency and the trap depth and how to decide proper construction when designing an rf atom chip.

physics.atom-ph↗