Optical preparation and measurement of atomic coherence at gigahertz bandwidth

We detail a method for the preparation of atomic coherence in a high density atomic medium, utilising a coherent preparation scheme of gigahertz bandwidth pulses. A numerical simulation of the preparation scheme is developed, and its efficiency in preparing coherent states is found to be close to unity at the entrance to the medium. The coherence is then measured non-invasively with a probe field.Comment: 7 pages, 5 figure

Electromagnetically induced transparency in a V-system with 87Rb vapor in the hyperfine Paschen–Back regime

We observe electromagnetically induced transparency (EIT) in a V-system in a thermal rubidium-87 vapour in the hyperfine Paschen-Back regime, realised with a 0.6 T axial magnetic field. In this regime energy levels are no longer degenerate and EIT features from different initial states are distinct, which we show produces a much cleaner feature than without a magnetic field. We compare our results to a model using the time-dependent Lindblad master equation, and having averaged over a distribution of interaction times, see good qualitative agreement for a range of pump Rabi frequencies. Excited state decay into both ground states is shown to play a prominent role in the generation of the transparency feature, which arises mainly due to transfer of population into the ground state not coupled by the probe beam. We use the model to investigate the importance of coherence in this feature, showing that its contribution is more significant at smaller pump Rabi frequencies

ElecSus: Extension to arbitrary geometry magneto-optics

We present a major update to ElecSus, a computer program and underlying model to calculate the electric susceptibility of an alkali-metal atomic vapour. Knowledge of the electric susceptibility of a medium is essential to predict its absorptive and dispersive properties. In this version we implement several changes which significantly extend the range of applications of ElecSus, the most important of which is support for non-axial magnetic fields (i.e. fields which are not aligned with the light propagation axis). Supporting this change requires a much more general approach to light propagation in the system, which we have now implemented. We exemplify many of these new applications by comparing ElecSus to experimental data. In addition, we have developed a graphical user interface front-end which makes the program much more accessible, and have improved on several other minor areas of the program structure

Absolute absorption on the potassium D lines: theory and experiment

We present a detailed study of the absolute Doppler-broadened absorption of a probe beam scanned across the potassium D lines in a thermal vapour. Spectra using a weak probe were measured on the 4S $\to$ 4P transition and compared to the theoretical model of the electric susceptibility detailed by Zentile et al (2015 Comput. Phys. Commun. 189 162–74) in the code named ElecSus. Comparisons were also made on the 4S $\to$ 5P transition with an adapted version of ElecSus. This is the first experimental test of ElecSus on an atom with a ground state hyperfine splitting smaller than that of the Doppler width. An excellent agreement was found between ElecSus and experimental measurements at a variety of temperatures with rms errors $\sim {10}^{-3}$. We have also demonstrated the use of ElecSus as an atomic vapour thermometry tool, and present a possible new measurement technique of transition decay rates which we predict to have a precision of ~$3\;\mathrm{kHz}$

Single-photon interference due to motion in an atomic collective excitation

We experimentally demonstrate the generation of heralded bi-chromatic single photons from an atomic collective spin excitation (CSE). The photon arrival times display collective quantum beats, a novel interference effect resulting from the relative motion of atoms in the CSE. A combination of velocity-selective excitation with strong laser dressing and the addition of a magnetic field allows for exquisite control of this collective beat phenomenon. The present experiment uses a diamond scheme with near-IR photons that can be extended to include telecommunications-wavelengths or modified to allow storage and retrieval in an inverted-Y scheme

Voigt transmission windows in optically thick atomic vapours: a method to create single-peaked line centre filters

Cascading light through two thermal vapour cells has been shown to improve the performance of atomic filters that aim to maximise peak transmission over a minimised bandpass window. In this paper, we explore the atomic physics responsible for the operation of the second cell, which is situated in a transverse (Voigt) magnetic field and opens a narrow transmission window in an optically thick atomic vapour. By assuming transitions with Gaussian line shapes and magnetic fields sufficiently large to access the hyperfine Paschen–Back regime, the window is modelled by resolving the two transitions closest to line centre. We discuss the validity of this model and perform an experiment which demonstrates the evolution of a naturally abundant Rb transmission window as a function of magnetic field. The model results in a significant reduction in two-cell parameter space, which we use to find theoretical optimised cascaded line centre filters for Na, K, Rb and Cs across both D lines. With the exception of Cs, these all have a better figure of merit than comparable single cell filters in literature. Most noteworthy is a Rb-D2 filter which outputs >92% of light through a single peak at line centre, with maximum transmission 0.71 and a width of 330 MHz at half maximum

Double-impulse magnetic focusing of launched cold atoms.

We have theoretically investigated three-dimensional focusing of a launched cloud of cold atoms using a pair of magnetic lens pulses (the alternate-gradient method). Individual lenses focus radially and defocus axially or vice versa. The performance of the two possible pulse sequences are compared and found to be ideal for loading both 'pancake' and 'sausage' shaped magnetic/optical microtraps. It is shown that focusing aberrations are considerably smaller for double-impulse magnetic lenses compared to single-impulse magnetic lenses. An analysis of clouds focused by the double-impulse technique is presented