Enhancement of Rydberg atom interactions using dc and ac Stark - PowerPoint PPT Presentation

Enhancement of Rydberg atom interactions using dc and ac Stark shifts Parisa Bohlouli-Zanjani �������������������������������������������������������������� �������������������������������� University of Virginia, Department of Physics 6/27/2011

Objective � Enhancement of interatomic interactions by electric field induced resonant energy transfer (RET) A + A ! B + C Motivations � Determining unknown atomic energy levels by dc field induced RET spectra � Using ac field induced RET for energy level determination where dc field can not be used � RET can be utilized in the implementation of dipole blockade 2

Summary of the materials to be discussed � Rydberg atoms � Experimental methodology � Magneto-Optical Trap (MOT), Selective Field Ionization (SFI) � Laser frequency stabilization � Dipole-Dipole interactions, RET � dc electric-field-induced RET � Estimation of g series quantum defect � Observation of ac electric-field-induced RET 3

Summary of the materials to be discussed � Rydberg atoms � Experimental methodology � Magneto-Optical Trap (MOT), Selective Field Ionization (SFI) � Laser frequency stabilization � Dipole-Dipole interactions, RET � dc electric-field-induced RET � Estimation of g series quantum defect � Observation of ac electric-field-induced RET 4

Rydberg atoms loosely bound electron circling ionic core. � Rydberg constant (13.5 eV) Ionization continuum Infinitely ionization potential many bound states quantum defect for Na these states have long lifetimes (eg. 17p of Na: 50 µ s ). � properties scale with n and can be exaggerated . � 5

Summary of the materials to be discussed � Rydberg atoms � Experimental methodology � Magneto-Optical Trap (MOT), Selective Field Ionization (SFI) � Laser frequency stabilization � Dipole-Dipole interactions, RET � dc electric-field-induced RET � Estimation of g series quantum defect � Observation of ac electric-field-induced RET 6

Experimental Methodology Form cold Rb atoms in a MOT for studies � between stationary atom � 1 mm 3 , 300 µ K , Rydberg atoms: 10 7 cm -3 Rydberg atom excitation using 480nm � frequency doubled Ti:sapphire laser Measurement and compensation of stray E and B fields using mwave transitions � between Rydberg states Do experiment … � Verify excitation using SFI technique � 10 Hz repetition rate � 7

Selective Field Ionization (SFI) detection of Rydberg atoms Field ionization pulse 400 slowly rising FIP ion signal (47s 1/2 & 47p 1/ 2 states) 300 200 voltage MCP signal Voltage (V) 100 47p 1/2 47p 1/2 � Use SFI to determine state 0 distribution in the trap. -100 47s 1/2 47s 1/2 -200 -6 0 2 4 6 8 10 12x10 time ( µ s) Time (s) 8

Rydberg Atom Excitation Ionization Continuum np ns nd Infinitely many bound states 46d 6s Energy ~ 480 nm 5p 3/2 Frequency doubled Ti:sapphire laser 5d ~ 780 nm Cooling & trapping transitions (Diode Laser) 5s 9

Summary of the materials to be discussed � Rydberg atoms � Experimental methodology � Magneto-Optical Trap (MOT), Selective Field Ionization (SFI) � Laser frequency stabilization � Dipole-Dipole interactions, RET � dc electric-field-induced RET � Estimation of g series quantum defect � Observation of ac electric-field-induced RET 10

Optical Transfer Cavity Stabilization using Tunable Sidebands of RF Current-Modulated Injection-Locked Diode Lasers Objective � Stabilize lasers at frequencies where direct locking to a reference line is not possible Motivation � High resolution optical spectroscopy for laser cooled Rydberg atom excitation.

Review / Alternative approaches Absolute frequency reference (Barger 1969) � ref. laser � Beat note locking trgt. PD � Practical up to a certain frequency laser difference feedback Scanning transfer cavity (TC) (Lindsay 1991, � ref. laser Rossi 2002) TC trgt. � Scanning rate limits the maximum error laser correction feedback � Sensitive to low frequency vibrations PC � Complexity of the fringe comparison ref. laser AOM Stabilized TC (Burghardt 1979, Plusquellic 1996) � (EOM) trgt. � Frequency shift using EOM or AOM laser TC feedback

A general frequency stabilization technique � Fabry--Perot TC stabilized using a tunable sideband from a current modulated injection locked diode laser. � Frequency shifts without using AOMs or EOMs. � Not limited to certain wavelengths � Tuning frequency with RF precision.

Experimental setup : PBS PBS fiber FR master laser λ /2 λ /2 λ λ λ λ λ λ 780nm λ /2 λ λ λ Rb PS slave locking -f m +f m laser control fiber PD circuit RF f m λ /2 PD R. Kowalski et al., λ /2 PBS Rev. Sci. Instrum. PBS 72, 2532 (2001). transfer cavity piezo fiber control Ti:Sapphire ring doubler to MOT circuit laser- 960 nm 480 nm 14

Rydberg atom excitation ( 85 Rb) 46d 5/2 0.6 (d) Averaged MCP signal (V) 46d 5/2 46d 3/2 119 MHz 46d 3/2 0.4 59.5 MHz (c) (c) (a) 0.2 (b) (d) (b) (a) 5p 3/2 0.0 385 THz cooling laser 780nm 5s 1/2 0 20 40 60 80 100 Target laser (960nm) frequency + offset (MHz) Autler –Townes splitting : B. K. Teo et al., Phys. Rev. A. 68, 053407 (2003). 15

140 Frequency stability 120 Frequency fluctuation of the � 100 target laser (Ti:sapphire, 960 nm) (a) unlocked MBR freq drift (MHz) (a) unlocked 80 � (a) unlocked 140 MHz � (b) locked < 0.25 MHz 60 1.0 drift (MHz) 0.0 40 -1.0 0 30 00 time(s) � Not limited to certain wavelengths 20 � Tuning frequency with RF 0 precision . (b) locked � Frequency shifts without using -20 AOMs or EOMs. 0 1000 2000 3000 time(s) 16

Summary of the materials to be discussed � Rydberg atoms � Experimental methodology � Magneto-Optical Trap (MOT), Selective Field Ionization (SFI) � Laser frequency stabilization � Dipole-Dipole interactions, RET � dc electric-field-induced RET � Estimation of g series quantum defect � Observation of ac electric-field-induced RET 17

Properties of Rydberg atoms - 3 n ¤ = n ¡ ± l P. Filipovicz et al. , Optica Acta, 32 , 1105 (1985) •

Electric Dipole-Dipole Interactions between Rydberg Atoms ¹ B ~ ¹ A ~ V dd = ~ ¹ A ¢~ ¹ B ¡ 3 (~ ¹ A ¢~ n)(~ ¹ B ¢~ n) ^ n ^ R 3 A B R A B � dipole-dipole interaction strong for Rydberg states -- even over long distances. � atoms temporarily excited to Rydberg states strongly interact due to dipole-dipole interaction -- but don’t interact when in ground state.

Resonant Energy Transfer (RET) through dipole-dipole interactions A + A ! A + A ! B + C B + C

Summary of the materials to be discussed � Rydberg atoms � Experimental methodology � Magneto-Optical Trap (MOT), Selective Field Ionization (SFI) � Laser frequency stabilization � Dipole-Dipole interactions, RET � dc electric-field-induced RET � Estimation of g series quantum defect � Observation of ac electric-field-induced RET 21

Resonance condition may be achieved using Stark effect: -298 20p -300 After excitation of 20s states: -314 20s Energy -316 20p signal (cm -1 ) -330 200 210 220 240 Electric field (V/cm) -332 19p -334 0 200 300 100 Electric field (V/cm) 22

Achieving resonance condition in Rb Rb Stark map - energies relative to 44d 5/2 44d 5=2 + 44d 5=2 ! 42f 5=2 + 46p 3=2 23

Mismatch as a function of n nd 5=2 + nd 5=2 ! (n + 2)p 3=2 + (n ¡ 2)f Consider the process: ¢ E m i sm at ch = E f ¡ E i ¢ E m i sm at ch Energy shifts of this magnitude can be easily obtained using the ac or dc Stark effect Energies determined using quantum defects from: J. N. Han et al. , PRA 74, 054502 (2006); W. H. Li et al. , PRA 67, 052502 (2003) 24

Observation of dc field induced RET at n = 44 44d 5=2 + 44d 5=2 ! 46p 3=2 + 42f ���� � �� 25

Observation of dc field induced RET at n = 32 32d 5=2 + 32d 5=2 ! 34p 5=2 + 30g

Resonant electric fields can be used to determine energy levels 32d 5=2 + 32d 5=2 ! 34p 5=2 + 30g unknown!! known energies ± g (n = 30) = 0:00405(6) 27

Lower n by 1 and process cannot be tuned into resonance nd 5=2 + nd 5=2 ! (n + 2)p 3=2 + (n ¡ 2)f 5=2;7=2 n = 44 n = 43 28

Can an ac field be used? Perturbative ac Stark effect Perturbative dc Stark effect X X ¢ E n = 1 E n s j < nj ¹ z js> j 2 j < nj ¹ z js> j 2 2" 2 ¢ E n = " 2 E 2 n s ¡ (~! ) 2 z E n s z s s ������������������ ��������������� ���$����� �������������� ������ E ns = E n ¡ E s ! > E ns s s ������ ������ ( ������"�� ) ! < E ns " z " z ω ���������!�"������������������������#

Summary of the materials to be discussed � Rydberg atoms � Experimental methodology � Magneto-Optical Trap (MOT), Selective Field Ionization (SFI) � Laser frequency stabilization � Dipole-Dipole interactions, RET � dc electric-field-induced RET � Estimation of g series quantum defect � Observation of ac electric-field-induced RET 30