Many-Body Effects in a Frozen Rydberg Gas Feng zhigang

outline  Introduction  Resonant Dipole-Dipole Energy Transfer in Frozen Rydberg Gas  Conclusion  Our experiment

Rydberg atoms are atoms that are excited to states of high principal quantum number n the first appearance of Rydberg atoms in the Balmer series of atomic H 1913 Bohr proposed his model of the H atom that related the Rydberg constant to the mass and charge of the electron High resolution spectroscopy was used in experiment to demonstrate the bizarre properties of Rydberg atoms Problem : not interpretation the properties of atoms near series limit There are simply no means of making Rydberg atoms efficiently enough

In the 1950s and 1960s Electron impact excitation and charge exchange excitations were the only available schemes of producing Rydberg atoms. These methods resulted in the spread of Rydberg population over many states. In the 1970s With the advent of tunable dye lasers, it became possible to produce samples of single-state Rydberg atoms (atoms excited to the same energy level). In the 1990s With laser cooling and trapping techniques development, opened new areas of research related to Rydberg atoms such as ultracold plasmas, quantum computing with cold neutral atoms and Rydberg, atom-surface interaction in atom- chip experiments.

Why

Applications of Rydberg atoms  Metrology  Micromaser and cavity QED  Atom-photon entanglement and quantum information  sensor for IR and THz radiation  IR streak camera  Electron targets

Resonant Diople-Diople Energy Transfer in Frozen Rydberg Gas

A frozen Rydberg gas is a sample of atoms with highly excited electronic states and very low temperature. In this experiments 85 Rb Temperature: T ~300µK The density of Rydberg atoms N d ~10 9 atoms/cm 3 Average velocity v~38cm/s Experiment time t~3µs Displacement △ R =vt~1µm Average interatomic distance R 0 ~(3/4N d ) 1/3 = 10µm. What is frozen Rydberg gas ?

Diode laser Linewidth 3MHz Power 10mW Diameter 5mm Atoms number 10 7 Density cm -3 Density 10 9 cm -3 Dye laser Linewidth 0.1cm -1 Rate 10% F=2 5S 1/2 780nm F=3 F’=4 F’=3 F’=2 F’=1 Trapping laser Repumping laser 5P 3/2 480nm 25S/33S

Energy transfer process 25S 1/2 +33S 1/2 →24P 1/2 +34P 3/2 Cross section At room temperature 300K Not density

The resonance linewidth Increase from 3.9 to 8.4MHz as the number density is increased from 0.19N 0 to N 0 Phys. Rev. Lett. 80, 249 (1998).

The typical observed linewidth, 5 MHz, is almost 3 orders of magnitude larger than the expected 12 kHz linewidth for a binary collision. Furthermore, the linewidths of the energy transfer resonances increase with number density, unlike those of binary collisional resonances. Similar broadening of Cs energy transfer resonances has been observed by Mourachko et al. reasons Electric filed Magnetic field others Photoionization Black body radiation Small separation atoms

How ? In the resonant dipole-dipole transfer process, there are three pairs dipole-dipole coupling. Rb 25S 1/2 +Rb 33S 1/2 →Rb 24P 1/2 +Rb 34P 3/2 (a) Rb 25S 1/2 +Rb 24P 1/2 →Rb 24P 1/2 +Rb 25S 1/2 (b) Rb 33S 1/2 +Rb 34P 3/2 →Rb 34P 3/2 +Rb 33S 1/2 (c) Responsible for the observed resonant energy transfer Only resonant at 3.0 and 3.4V/cm Strength : Resonant at all electric field Strength: (b) (c)

Interpretation U: V: S: 25S P: 24P S / : 33S P / :34P

The process has some analogy to autocatalitic processes in chemistry: the fluctuations corresponding to pairs of atoms at small separations are responsible for the ignition of the reaction and the diffusion evacuates the reaction products. The linewidth is determined by the coupling of the close atoms There are too few of these atoms, though, to give the magnitude of the signal observed. Development of the signal and its magnitude are determined by the couplings due to the average spacing. Rb 25S 1/2 +Rb 33S 1/2 →Rb 24P 1/2 +Rb 34P 3/2 Rb 25S 1/2 +Rb 24P 1/2 →Rb 24P 1/2 +Rb 25S 1/2 Rb 33S 1/2 +Rb 34P 3/2 →Rb 34P 3/2 +Rb 33S 1/2

Rb 34S 1/2 +Rb 34P 3/2 →Rb 34P 3/2 +Rb 34S 1/2

33S 25S MW pulse 33S—34S Filed ionization pulse Static Electric Filed Pulse -0.8V/cm V/cm Time 3.25V/cm

N[Rb(25S)]= N[Rb(33S)] Rb 25S 1/2 +Rb 33S 1/2 →Rb 24P 1/2 +Rb 34P 3/2 (a) Rb 25S 1/2 +Rb 24P 1/2 →Rb 24P 1/2 +Rb 25S 1/2 (b) Rb 33S 1/2 +Rb 34P 3/2 →Rb 34P 3/2 +Rb 33S 1/2 (c) Rb 34S 1/2 +Rb 34P 3/2 →Rb 34P 3/2 +Rb 34S 1/2 V 2 =16V 3 N[Rb(25S)]µ 2 ≤ N[Rb(33S)]µ´ 2

34S density 0 to 10 9 atoms/cm 3 line width From 6 to 13.5 MHZ 0.35 The higher 34S density not only Increase the width resonances But amplitudes

conclusion 1 In frozen Rydberg gas, resonant energy transfer is not a binary process but a many- atoms process. 2 Resonance linewidth and the line shape changes with density of Rydberg atoms. 3 The linewidth is determined by the coupling of the close atoms, development of the signal and its magnitude are determined by the couplings due to the average spacing 4 Introducing an additional 34s state into the resonant energy-transfer process provides decisive evidence that the dipole-dipole couplings in a frozen Rydberg gas have the nature of a many-body interaction.

Our experiment

6P 3/2 6S 1/2 852nm F=4 F=3 F’=5 F’=4 F’=3 F’=2 Trapping laser Repumping laser nS/nD 511nm

852nm laser DL100 SAS1 laser DL100 SAS2 Trapping beams Repumping beam Dye laser AOM PBS YAG PBS AOM MOT1 Wavelength Meter SP OI

Thank You !