Towards a three-step laser excitation of rubidium Rydberg states for use in a microwave CQED single-atom detector
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This document discusses techniques for three-step laser excitation of rubidium atoms to produce Rydberg states for use in single-atom detection. It summarizes the experimental techniques used, including polarization spectroscopy to excite atoms to the 5D5/2 state and electromagnetically induced transparency to enhance the weaker second transition. Precise control of the laser frequencies was achieved, with Allan deviations of 30kHz and 45kHz over 1 hour, representing errors of less than 0.003% of the natural linewidths. The goal was to excite rubidium atoms to the 63P3/2 Rydberg state for single-atom detection applications.
Towards a three-step laser excitation of rubidium Rydberg states for use in a microwave CQED single-atom detector
- 1. BEN CATCHPOLE Towards a three-step laser excitation of rubidium Rydberg states for use in a microwave CQED single- atom detector
- 2. INTRODUCTION MOTIVATION - Applications for Rydberg states - Single-atom detection (S.A.D.) THEORETICAL BACKGROUND - Rydberg production - Doppler free spectroscopy - Fine and Hyperfine structure EXPERIMENTAL TECHNIQUES - Polarisation spectroscopy - Electromagetically induced transparency (EIT) RESULTS OVERVIEW
- 3. AIM - Three step laser excitation to produce 63P3/2 Rydberg states for SAD ACHIEVEMENTS - Doppler-free spectroscopic techniques applied to excite ground- state rubidium atoms to the 5D5/2 hyperfine excited state. - Techniques allowed for precise control of laser frequency: - Allan Deviations of 30kHz and 45kHz for first two transitions over ~ 1hour, this represents as little as 0.0029% and 0.003% of the 10.3±0.1MHz and ~14MHz natural transition linewidths, respectively. INTRODUCTION
- 4. MOTIVATION Rydberg atoms, with a very high principal quantum number (n), large dipole moments and long transition lifetime can be used in a wide- range of experimental setups… - One-atom maser (Micromaser) (1985) - Collapse/revival of VROs (1987) - Verification of quantised EM field with VROs (1996) - Production of ‘number’ states on demand – Trapping - State reduction - Rydberg ‘blockades’ ~(2000) - Observation of field state collapse with QND measurements (2007) - Birth, life and death of a single photon (2007) - ‘Freezing’ evolution of cavity field with Quantum Zeno effect (2008) - Sensitive detection of microwave photons
- 5. - Transmission spectrum of cavity split by presence of atom (normal mode splitting), without an atom only a single peak is observed. - When atom and cavity are tuned into resonance mixing of the states prduces new Eigenfrequencies for the atom-field state - Demonstrated sufficient sensitivity for SAD
- 6. DOPPLER EFFECTS DOPPLER BROADENING OF SPECTRAL SIGNAL - Due to thermal motion of the atomic vapour - Gaseous atoms have a Maxwell-Boltzmann velocity distribution - Atoms move randomly in all directions - Each velocity component takes a distibution of values - This range of velocities produces a range of Doppler-shifts - Cumulative effect is inhomogeneous line broadening of spectral signal DOPPLER-FREE SPECTROSCOPY - Collimated atomic beam spectroscopy (1942) - Saturated absorption spectroscopy (1971)
- 7. SAS SATURATED ABSORPTION SPECTROSCOPY (SAS) - Velocity-selective saturation of absorption Doppler free signal - Laser divided into a ‘PUMP’ and less intense ‘PROBE’ - (Iprobe<<Isat) and (Ipump>Isat) - PUMP ‘burns’ a hole in lower level population density - Means probe encounters less ground state atoms – reduced absorption - Pump interacts with atoms in the velocity class: - Far from resonance the counter-propagating beams interact with a completely different velocity class - Close to resonance the difference between the laser and the transition is ~0, therefore both beams interact with the same ~0 velocity class - As the hole is burn into the zero-velocity class of atoms, and only these contribute to the spectral signal, the lamb dip is free from Doppler broadening and the spectra is DOPPLER-FREE
- 8. FINE AND HYPERFINE STRUCTURE - GROSS structure described by solutions to the Schrodinger equation - FINE structure due to SPIN-ORBIT interaction - HYPERFINE structure due to SPIN-SPIN interaction
- 9. GROSS STRUCTURE - As an alkali metal, ground state rubidium has a single valence electron in the outer 5s orbital. FINE STRUCTURE (due to Spin-Orbit interaction) - Caused by the splitting of ‘gross structure’ atomic energy levels - ‘orientation energy’ – as it is determined by the relative orientation of two magnetic vectors. - S: total ELECTRONIC SPIN angular momentum - L: total ORBITAL angular momentum - J represents the TOTAL ELECTRONIC angular momentum, which takes values of |L-S| to L+S. - Both L and S sum to zero for closed orbitals, consequently only the valence electron contributes… FINE STRUCTURE (2s+1)LJ (1s22s22p63s23p63d104s24p6 5s) J=L+S 5s state(L=0),(S=1/2)5S1/2 5p state(L=1),(S=1/2)5P1/2 5P3/2
- 10. (due to Spin-Spin interaction) HYPERFINE STRUCTURE - Caused by splitting of fine structure energy levels - Also an ‘orientation energy’, due to two magnetic dipoles in different orientations. - NUCLEAR SPIN angular momentum (I) is proportional to nuclear structure – determines magnetic moment of nucleus - F represents the TOTAL ATOMIC angular momentum which takes values |J-I| to J+I and determines the HYPERFINE energy levels.HYPERFINE STRUCTURE 5s state(L=0),(S=1/2)5S1/2 5P3/2 5p state(L=1),(S=1/2)5P1/2 F=I+J
- 11. (due to Spin-Spin interaction) HYPERFINE STRUCTURE - The most abundant (72%) isotope, 85Rb has a total nuclear spin I=5/2 - Consequently have 2 possible values of angular momentum for the 5S1/2 ground state and 4 for the excited 5P3/2 state, due to non- zero L value. - Only specfic transitions are allowed due to dipole selection rules (∆F=0,±1) – indicated by arrows. (red arrows are enhanced transitions)HYPERFINE STRUCTURE F=I+J 5S1/2 (5/2)±1/2 (2,3) 5P1/2 (5/2)±1/2 (2,3) 5P3/2 (5/2)±1/2 (2,3) (5/2)±3/2 (1,4)
- 12. ~1260 nm EXPERIMENTAL TECHNIQUES - The specific excitation pathway utilised during the experiment - 780.24 nm transition: 5S1/2 (F=3) and 5P3/2 (F=4) hyperfine levels - 775.98 nm transition: 5P3/2 (F=4) and 5D5/2 (F=5) hyperfine levels - From 5D5/2 (F=5), mF=5, dipole selection rules (∆l=±1 and ∆j=0,±1) dictate that nP3/2, nF5/2 and nF7/2 Rydberg states are attainable
- 13. EXPERIMENTAL TECHNIQUES POLARISATION SPECTROSCOPY (5S1/25P3/2 transition) - Form of SAS, based on light-induced BIREFRINGENCE and DICHROISM - Circularly polarised PUMP used to generate OPTICAL ANISTROPY, which is interrogated by the linearly polarised PROBE - Linearly polarised PROBE can be decomposed into 2 circularly polarised beams, rotating in opposite directions, these encounter different refractive indicies and absorption coefficients - Beam splitter used to seperate |H> and |V> components - Intensity difference provides polarisation spectroscopy signal IMPROVED SNR & NO NEED FOR FREQUENCY MODULATION!
- 17. ELECTROMAGNETICALLY INDUCED TRANSPARENCY (EIT) EXPERIMENTAL TECHNIQUES - The second 776nm transition is much weaker (longer atomic lifetime) – therefore utilised QUANTUM AMPLIFICATION (QA), whereby a lifetime difference was used to create an EIT. - Produced an enhanced first step transmission signal which is a function of second step detuning- QA: detection of a weak resonance signal via the response of a strong atomic transition when the transitions share a common state - Excitation to the 5D5/2 state hinders multiple absorption-emission cycles on the 5S-5P transition, leading to a visibly enhanced first-step transmission peak known as a ‘reduced absorption peak’ - Lifetimes: (5D5/2=238.5ns) and (5P3/2=26.24ns) - Therefore EIT peak ~10x larger than optically available
- 18. - Typical 5P3/2 (F=4) to 5D5/2 (F=5) spectral feature detected using QA, consequently the signal represents a first-step reduced absorption peak and dispersion-shaped error signal generated through frequency modulation of the spectral feature.