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European Frequency and Time Forum

Rydberg spin-squeezing for a strontium optical lattice clock

Elizabeth M. Bridge, D. Boddy, D. P. Sadler, Alistair D. Bounds, Charles S. Adams, M. P. A. Jones, L. I. R. Gil, Rick Mukherjee, Thomas Pohl

Published Jun 1, 2014• 0 citations
Publisher

Abstract

We present a new technique for achieving high levels of squeezing in strontium optical lattice clocks using the long-range van der Waals interactions between high-lying Rydberg states. This technique requires only one additional laser and could provide over 10 dB of squeezing in large atomic ensembles, in just a few microseconds, without significantly affecting the subsequent clock interrogation. We outline this spin-squeezing technique and report on our experimental progress towards demonstrating this method. Significant experimental milestones include development of a versatile UV laser system for demonstrating this technique, and the first observation of the Rydberg blockade effect in a divalent atom.

DOI
10.1109/eftf.2014.7331530

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We present a new technique for achieving high levels of squeezing in strontium optical lattice clocks using the long-range van der Waals interactions between high-lying Rydberg states. This technique requires only one additional laser and could provide over 10 dB of squeezing in large atomic ensembles, in just a few microseconds, without significantly affecting the subsequent clock interrogation. We outline this spin-squeezing technique and report on our experimental progress towards demonstrating this method. Significant experimental milestones include development of a versatile UV laser system for demonstrating this technique, and the first observation of the Rydberg blockade effect in a divalent atom.
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We report on recent realization of an optical lattice clock operating on the1S0-3P0transition in88Sr, at LENS laboratories. The clock transition is excited with the technique of magnetic field-induced spectroscopy. New experimental techniques has also been developed in order to simplifies the clock spectroscopy in Sr atoms. The first new method helps in the first search of the clock transition without the use of extensive frequency metrology hardware and in particular optical frequency combs. This technique exploits a near coincidence in the atomic wavelengths of the1S0-3P0clock and1S0-3P1second stage cooling transitions in Sr, which are only 5 THz far apart. This coincidence enables the use of an optical (transfer) cavity to reference the frequency of the clock transition relative to that of the much stronger cooling transition. Secondly we reduce the complexity of the experimental setup by using only semiconductor laser sources in the apparatus. With this setup, about 10488Sr atoms are trapped in a 1D lattice formed by 200 mW of radiation tuned near the magic wavelength at 813 nm. We will present a first uncertainty budget for our optical lattice clock based on88Sr with particular attention to density dependent collisions, which led to an unexpectedly high signal contrast for long interaction times. In view of an absolute frequency measurement of clock transition we'll also present recent experimental results on optimization of an home made Ti:Sa optical frequency comb. Additionally, we anticipate that the simplification of the experimental setup presented will help address a wider range of applications including those requiring transportable devices. Along these lines we will report progress on the realization of the first transportable Sr optical lattice clock.
Strontium optical lattice clocks at JILA recently demonstrated record-high accuracy and stability. These advances were enabled by an ultrastable laser with fractional frequency stability of 1x10-16 at 1 second. This laser allows us to study systematic shifts of the 1S0 to 3P0 clock transition with unprecedented precision. Density-dependent frequency shifts represent an unavoidable perturbation for clocks based on many atoms. Our studies of atomic interactions in an optical lattice clock system uncover the nature of these interactions and reveal important many-body atomic correlation effects in this open quantum system. By extending our measurements to all ten nuclear-spin sublevels of the clock states, we observe the first direct evidence of SU(N) symmetric interactions in alkaline earth(-like) atoms. Using the techniques we developed in these studies, we also demonstrate a novel technique for measuring the frequency noise spectrum of an ultrastable laser. We discuss designs for the future direction of our experiment which will place 87Sr atoms within a high finesse cavity that is resonant on the 1S0 to 3P1 transition. We will use this system to study collective effects in cavity quantum electrodynamics. Most notably, strong atom-cavity coupling can enhance the spectroscopic sensitivity of our clock by creating spin-squeezed states via quantum non-demolition measurements. As a precursor to future work studying cavity-mediated collective behavior, we use the unique atomic structure of 88Sr to investigate free-space retarded dipolar coupling in an optically thick sample of atoms.
This thesis details the development of the pre-requisite experimental tools to create a proof-of-principle spin-squeezed atomic clock based upon an array of individual strontium atoms using Rydberg-dressed interactions. We experimentally and theoretically study Rydberg-dressing in a strontium narrow-line MOT, demonstrating that it is possible to coherently admix a Rydberg state into the narrow intercombination transitions of strontium. This work is based upon a quantitative semi-classical Monte-Carlo model of a strontium narrow-line MOT, where the combination of a quantum treatment of the light scattering process with a Monte-Carlo simulation of the atomic motion leads to a quantitative description of the spatial, thermal and temporal dynamics of the narrow-line MOT. By performing calculations of the dynamic polarisability of all the states relevant to laser cooling strontium, we have designed and constructed a new experimental apparatus to facilitate the creation of a microtrap of strontium. We observe and characterise the frst known microtrap of strontium and outline the next steps towards the creation of an array of single atoms. Due to the creation of Rydberg atoms in the strontium microtrap, understanding ionisation and interaction mechanisms may be of signifcant importance. We therefore study Rydberg ionisation mechanisms in a thermal beam of strontium atoms using simultaneous measurements of Rydberg EIT and spontaneously created ions or electrons. By connecting the optical and electrical signals using the optical Bloch equations, we are able to determine the dominant ionisation mechanisms of Rydberg atoms in the thermal beam. We also report the frst observations of optical and electrical bistability, which may shed further light onto the origin of bistability in atom vapours.