Nanoscale guiding for cold atoms based on surface plasmons along the tips of metallic wedges

We propose a novel scheme to guide neutral cold atoms in a nanoscale region based on surface plasmons （SPs） of one pair and two pairs of tips of metallic wedges with locally enhanced light intensity and sub-optical wavelength resolution. We analyze the near-field intensity distribution of the tip of the metallic wedge by the FDTD method, and study the total intensity as well as the total potential of optical potentials and van der Waals potentials for 87 Rb atoms in the light field of one pair and two pairs of tips of metallic wedges. It shows that the total potentials of one pair and two pairs of tips of metallic wedges can generate a gravito-optical trap and a dark closed trap for nanoscale guiding of neutral cold atoms. Guided atoms can be cooled with efficient intensity-gradient Sisyphus cooling by blue-detuned light field. This provides an important step towards the generation of hybrid systems consisting of isolated atoms and solid devices.

Continuously transferring cold atoms in caesium double magneto-optical trap

We have established a caesium double magneto-optical trap （MOT） system for cavity-QED experiment, and demonstrated the continuous transfer of cold caesium atoms from the vapour-cell MOT with a pressure of - 1 × 10^-6 Pa to the ultra-high-vacuum （UHV） MOT with a pressure of - 8 × 10^-8 Pa via a focused continuous-wave transfer laser beam. The effect of frequency detuning as well as the intensity of the transfer beam is systematically investigated, which makes the transverse cooling adequate before the atoms leak out of the vapour-cell MOT to reduce divergence of the cold atomic beam. The typical cold atomic flux got from vapour-cell MOT is - 2 × 10^7 atoms/s. About 5 × 10^6 caesium atoms are recaptured in the UHV MOT.

Optimal transport of cold atoms by modulating the velocity of traps

This work experimentally demonstrates a new method of optimizing the transport of cold atoms via modulating the velocity profile imposed on a magnetic quadrupole trap.The trap velocity and corresponding modulation are controlled by varying the currents of two pairs of anti-Helmholtz coils.Cold 87Rb atoms are transported in a non-adiabatic regime over 22 mm in 200 ms.For the transported atoms their final-vibration amplitude dependences of modulation period number,depth,and initial phase are investigated.With modulation period n = 5,modulation depth K = 0.55,and initial phase φ = 0,cold atom clouds with more atom numbers,smaller final-vibration amplitude,and lower temperature are efficiently transported.Theoretical analysis and numerical simulation are also provided,which are in good agreement with experimental results.

Comparison of two absorption imaging methods to detect cold atoms in magnetic trap

Two methods of absorption imaging to detect cold atoms in a magnetic trap are implemented for a high-precision cold atom interferometer.In the first method,a probe laser which is in resonance with a cycle transition frequency is used to evaluate the quantity and distribution of the atom sample.In the second method,the probe laser is tuned to an open transition frequency,which stimulates a few and constant number of photons per atom.This method has a shorter interaction time and results in absorption images which are not affected by the magnetic field and the light field.We make a comparison of performance between these two imaging methods in the sense of parameters such as pulse duration,light intensity,and magnetic field strength.The experimental results show that the second method is more reliable when detecting the quantity and density profiles of the atoms.These results fit well to the theoretical analysis.

Simulation of anyons by cold atoms with induced electric dipole moment

We show that it is possible to simulate an anyon by a trapped atom which possesses an induced electric dipole moment in the background of electric and magnetic fields in a specific configuration.The electric and magnetic fields we applied contain a magnetic and two electric fields.We find that when the atom is cooled down to the limit of the negligibly small kinetic energy,the atom behaves like an anyon because its angular momentum takes fractional values.The fractional part of the angular momentum is determined by both the magnetic and one of the electric fields.Roles electric and magnetic fields played are analyzed.

Oscillation of the spin-currents of cold atoms on a ring due to light-induced spin–orbit coupling

The evolution of two-component cold atoms on a ring with spin-orbit coupling has been studied analytically for the case with N noninteracting particles. Then, the effect of interaction is evaluated numerically via a two-body system. Two cases are considered： （i） Starting from a ground state the evolution is induced by a sudden change of the laser field, and （ii） the evolution starting from a superposition state. Oscillating persistent spin-currents have been found. A set of formulae have been derived to describe the period and amplitude of the oscillation. Based on these formulae the oscillation can be well controlled via adjusting the parameters of the laser beams. In particular, it is predicted that movable stripes might emerge on the ring.

Investigation of ultracold atoms and molecules in a dark magneto-optical trap

In this paper, ultracold atoms and molecules in a dark magneto-optical trap （MOT） are studied via depumping the cesium cold atoms into the dark hyperfine ground state. The collision rate is reduced to 0.45 s-1 and the density of the atoms is increased to 5.6 × 1011 cm-3 when the fractional population of the atoms in the bright hyperfine ground state is as low as 0.15. The vibrational spectra of the ultracold cesium molecules are also studied in a standard MOT and in a dark MOT separately. The experimental results are analyzed by using the perturbative quantum approach.

Ultranarrow bandwidth Faraday atomic filter approaching natural linewidth based on cold atoms

An ultranarrow bandwidth Faraday atomic filter is realized based on cold 87Rb atoms. The atomic filter operates at 780 nm on the 52 S1/2, F = 2 to 52 P3/2, F’= 3 transition with a bandwidth of 7.1(8) MHz, which is approaching the natural linewidth of the transition. The peak transmission achieves 2.6(3)% by the multi-pass probe method. This atomic filter based on cold atoms may find potential applications in self-stabilizing lasers in the future.

Two-dimensional novel optical lattices with multi-well traps for cold atoms or molecules

We propose some new schemes to constitute two-dimensional （2D） array of multi-well optical dipole traps for cold atoms （or molecules） by using an optical system consisting of a binary 7r-phase grating and a 2D array of rectangle microlens. We calculate the intensity distribution of each optical well in 2D array of multi-well traps and its geometric parameters and so on. The proposed 2D array of multi-well traps can be used to form novel 2D optical lattices with cold atoms （or molecules）, and form various novel optical crystals with cold atoms （or molecules）, or to perform quantum computing and quantum information processing on an atom chip, even to realize an array of all-optical multi-well atomic （or molecular） Bose- Einstein condensates （BECs） on an all-optical integrated atom （or molecule） chip.

Simulating cyclotron-Bloch dynamics of a charged particle in a 2D lattice by means of cold atoms in driven quasi-lD optical lattices

Quantum dynamics of a charged particle in a two-dimensional （2D） lattice subject to magnetic and electric fields is a rather complicated interplay between cyclotron oscillations （the case of vanishing electric field） and Bloch oscillations （zero magnetic field）, details of which has not yet been com- pletely understood. In the present work we suggest to study this problem by using cold atoms in optical lattices. We introduce a one-dimensional （1D） model which can be easily realized in labora- tory experiments with quasi-lD optical lattices and show that this model captures many features of the cyclotron-Bloch dynamics of the quantum particle in 2D square lattices.

Electromagnetically induced transparency in a Zeeman-sublevels Λ-system of cold ^87Rb atoms in free space

We report the experimental investigation of electromagnetically induced transparency （EIT） in a Zeeman-sublevels A-type system of cold 87Rb atoms in free space. We use the Zeeman substates of the hyperfine energy states 52 S 1/2, F =- 2 and 52P3/2, F1 = 2 of 87Rb D2 line to form a A-type EIT scheme. The EIT signal is obtained by scanning the probe light over 1 MHz in 4 ms with an 80 MHz arbitrary waveform generator. More than 97% transparency and 100 kHz EIT window are observed. This EIT scheme is suited for an application of pulsed coherent storage atom clock （Yan B, et al. 2009 Phys. Rev. A 79 063820）.

A novel controllable double-layer magnetic lattice with cold atoms

We propose a novel array of controllable double-well magnetic microtraps for cold atoms by using an array of square current-carrying wires and two additional bias magnetic fields. Arrays of double layer magneto optical traps (MOTs) and Ioffe traps can be constructed by using same wire configurations and different currents and bias fields. Furthermore, the array of double-well magnetic microtraps can be continuously evolved as an array of single-well magnetic microtraps by reducing the currents in the wires. Our study shows that our scheme can be used to realize a controllable double-layer magnetic lattice with cold atoms, to form array of Bose-Einstein condensations (BECs), or to study atom interference, and so on.

Integrated, reliable laser system for an ^(87)Rb cold atom fountain clock

We designed, assembled, and tested a reliable laser system for ^(87)Rb cold atom fountain clocks. The laser system is divided into four modules according to function, which are convenient for installing, adjusting, maintaining, and replacing of the modules. In each functional module, all optical components are fixed on a baseplate with glue and screws, ensuring the system's structural stability. Mechanical stability was verified in a 6.11g RMS randomvibration test, where the change in output power before and after vibration was less than 5%. Thermal stability was realized by optimizing of the structure and appropriate selection of component materials of the modules through thermal simulation. In the laser splitting and output module, the change in laser power was less than 20% for each fiber in thermal cycles from 5℃ to 43℃. Finally,the functionality of the laser system was verified for a rubidium fountain clock.

Study of optical clocks based on ultracold ^171Yb atoms

The optical atomic clocks have the potential to transform global timekeeping,relying on the state-of-the-art accuracy and stability,and greatly improve the measurement precision for a wide range of scientific and technological applications.Herein we report on the development of the optical clock based on 171Yb atoms confined in an optical lattice.A minimum width of 1.92-Hz Rabi spectra has been obtained with a new 578-nm clock interrogation laser.The in-loop fractional instability of the 171Yb clock reaches 9.1×10-18 after an averaging over a time of 2.0×104 s.By synchronous comparison between two clocks,we demonstrate that our 171Yb optical lattice clock achieves a fractional instability of 4.60×10-16/√τ.

Intense source of cold cesium atoms based on a two-dimensional magneto–optical trap with independent axial cooling and pushing

We report our studies on an intense source of cold cesium atoms based on a two-dimensional（2D） magneto–optical trap（MOT） with independent axial cooling and pushing.The new-designed source,proposed as 2D-HP MOT,uses hollow laser beams for axial cooling and a thin pushing laser beam to extract a cold atomic beam.With the independent pushing beam,the atomic flux can be substantially optimized.The total atomic flux maximum obtained in the 2D-HP MOT is4.02 × 1010atoms/s,increased by 60 percent compared to the traditional 2D＋MOT in our experiment.Moreover,with the pushing power 10 μW and detuning 0Γ,the 2D-HP MOT can generate a rather intense atomic beam with the concomitant light shift suppressed by a factor of 20.The axial velocity distribution of the cold cesium beams centers at 6.8 m/s with an FMHW of about 2.8 m/s.The dependences of the atomic flux on the pushing power and detuning are studied in detail.The experimental results are in good agreement with the theoretical model.

Single-photon-level light storage with distributed Rydberg excitations in cold atoms

We present an improved version of the superatom(SA)model to examine the slow-light dynamics of a few-photons signal field in cold Rydberg atoms with van der Waals(vdW)interactions.A main feature of this version is that it promises consistent estimations on total Rydberg excitations based on dynamic equations of SAs or atoms.We consider two specific cases in which the incident signal field contains more photons with a smaller detuning or less photons with a larger detuning so as to realize the single-photon-level light storage.It is found that vdW interactions play a significant role even for the slow-light dynamics of a single-photon signal field as distributed Rydberg excitations are inevitable in the picture of dark-state polariton.Moreover,the stored(retrieved)signal field exhibits a clearly asymmetric(more symmetric)profile because its leading and trailing edges undergo different(identical)traveling journeys,and higher storage/retrieval efficiencies with well preserved profiles apply only to weaker and well detuned signal fields.These findings are crucial to understand the nontrivial interplay of single-photon-level light storage and distributed Rydberg excitations.

Chiral p-wave pairing of ultracold fermionic atoms due to a quadratic band touching

We study the superfuild ground state of ultracold fermions in optical lattices with a quadratic band touching. Examples are a checkerboard lattice around half filling and a kagome lattice above one third filling. Instead of pairing between spin states, here we focus on pairing interactions between different orbital states. We find that our systems have only odd-parity （orbital） pairing instability while the singlet （orbital） pairing instability vanishes thanks to the quadratic band touching. In the mean field level, the ground state is found to be a chiral p-wave pairing superfluid （mixed with finite f-wave pairing order-parameters） which supports Majorana fermions.

Demonstration of a cold atom beam splitter on atom chip

We report an experimental demonstration of a new scheme to split cold atoms on an atom chip. The atom chip consists of a U-wire and a Z-wire. The cold atom cloud is initially loaded and prepared in the Z-trap, which is split into two separate parts by switching on the current of the U-wire. The two separate atom clouds have a distance more than one millimeter apart from each other and show almost symmetrical profiles, corresponding to about a 50/50 splitting ratio.

Photostop of iodine atoms from electrically oriented ICl molecules

The dynamics of photostopping iodine atoms from electrically oriented ICI molecules was numerically studied based on their orientational probability distribution functions. Velocity distributions of the iodine atoms and their production rates were investigated for orienting electrical fields of various intensities. For the IC1 precursor beams with an initial rotational temperature of ~ 1 K, the production of the iodine atoms near zero speed will be improved by about ~ 5 times when an orienting electrical field of ~ 200 kV/cm is present. A production rate of ~ 0.5%0 is obtained for photostopped iodine atoms with speeds less than 10 m/s, which are suitable for magnetic trapping. The electrical orientation of IC1 precursors and magnetic trapping of photostopped iodine atoms in situ can be conveniently realized with a pair of charged ring magnets. With the maximal value of the trapping field being ~ 0.28 T, the largest trapping speed is ~ 7.0 m/s for the iodine atom.

High-performance coherent population trapping clock based on laser-cooled atoms

We present a coherent population trapping clock system based on laser-cooled^(87)Rb atoms.The clock consists of a frequency-stabilized CPT interrogation laser and a cooling laser as well as a compact magneto-optical trap,a highperformance microwave synthesizer,and a signal detection system.The resonance signal in the continuous wave regime exhibits an absorption contrast of~50%.In the Ramsey interrogation method,the linewidth of the central fringe is31.25 Hz.The system achieves fractional frequency stability of 2.4×10^(-11)/(√τ),which goes down to 1.8×10^(-13)at 20000 s.The results validate that cold atom interrogation can improve the long-term frequency stability of coherent population trapping clocks and holds the potential for developing compact/miniature cold atoms clocks.