DON26BZ01-NV037 TITLE: Synthetic Alkali Atom Vapor Density for Atom-Based Sensors

OUSW (R&E) CRITICAL TECHNOLOGY AREA(S): Quantum and Battlefield Information Dominance (Q-BID)

COMPONENT TECHNOLOGY PRIORITY AREA(S): Integrated Sensing and Cyber;Microelectronics;Quantum Science

PROJECTED CMMC LEVEL REQUIREMENT: Level 2 (Self)

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws.

OBJECTIVE: Simplify the thermal management of practical atom-based quantum sensors based on alkali atoms by creating a passive atom source operated at thermal equilibrium based on a synthetic alkali vapor density for rubidium or cesium atoms.

DESCRIPTION: Quantum sensors based on atoms offer the opportunity to produce measurements with excellent sensitivity or long-term stability, making them attractive use in atomic clocks, magnetometers, or inertial sensors. In these sensors, the atomic vapor represents the sensing media where variations in signal magnitude from fluctuations in atom number can lead to instability or loss of sensitivity. Maintaining consistent signal throughout environmental conditions represents one of several key design criteria for atom-based sensors for use outside the laboratory.

Many atom-based sensors rely on heavy alkali atoms, specifically rubidium and cesium. This is because of the simplified, hydrogen-like energy level structure, the availability of narrow-linewidth semiconductor diode lasers on the relevant D1 (795/895 nm) and D2 (780/852 nm) transitions, the accessibility of commercial microwave electronics at the 3-10 GHz hyperfine splittings, and the ease of production of vapor phase atoms at modest temperatures. The temperature dependence of the alkalis [Ref 1] leads to thermal stabilization at 80-130°C (ideal for vapor cells at 10e12-10e14/cc) or closer to room temperature (ideal for atom trapping at 10e8-10e10/cc). These temperatures rarely align with thermal profiles of other aspects of the system, requiring additional design at the expense of size, weight, and power (SWaP).

Active approaches to alkali regulation have been demonstrated to manipulate the vapor to a non-equilibrium state. These approaches involve forced chemical reactions, intercalated graphite, alkali impregnated materials glasses [Refs 2,3]. In each case, a feedback loop must respond to measurements of the vapor density, leading to extra sensor complexity.

An equilibrium vapor density represents the simplest atom source which can be synthetically adjusted to an elevated temperature through a mixture [Ref 4]. Here, a primary species mixed with a secondary species reduces the equilibrium vapor density of both species by the mixing ratio following Raoult’s Law [Ref 5]. Selecting a lower vapor density secondary species limits the negative impact of additional atom-atom collisions. Such an approach can be applied to laser-cooled systems in addition to vapor cells to enable equilibrium operation at elevated system temperature, providing tight thermal regulation at low power.

PHASE I: Develop and demonstrate a method to produce a predetermined mixture of primary and secondary alkali species allowing for reduction of equilibrium vapor density of the primary species. Mixtures consistent with supporting laser cooling at elevated temperatures from 30-85°C should be demonstrated corresponding to ~10-10,000× reductions in the primary species. Spectroscopic (or equivalent) determinations of the primary species density in the mixture should be evaluated against unmixed samples of the primary alkali species. A detailed synthesis approach for each mixture along with vapor density evaluations will be submitted.

In the Phase I Option, if exercised, stability of the mixtures against thermal cycling should be demonstrated for the mixtures produced in the Phase I Base.

PHASE II: Produce mixtures capable of supporting laser cooling and trapping at elevated temperatures over the 30-85°C range. Mixtures will be produced in or transferred into chambers that support optical access, magnetic fields, and ultra-high vacuum conditions compatible with atom trapping for evaluation. Spectroscopic (or equivalent) evaluation of the primary alkali reduction will be determined as in Phase I. In addition, atom trapping performance will be evaluated to determine number of atoms and loading time constant at a range of temperatures around the target temperature. The proposer may partner with other organizations if atom-trapping evaluation capability is not available in house. A plan to produce delivery mechanisms for mixtures in a variety of warm atom and cold atom scenarios will be submitted.

Deliver at a minimum three (3) samples (containing > 1 mg each) of the atom-trapping material in a proposed delivery mechanism to the Navy at the conclusion of Phase II.

PHASE III DUAL USE APPLICATIONS: Based on the demonstrations and continual advancement of laser cooling technologies, the atom source should lead to dramatic improvements in the SWaP of cold atom systems. Support the Navy in transitioning the technology to Navy use.

The end product technology could be leveraged to adapt atom-based sensors to a variety of thermal environments to support biomedical, communications, and navigation applications.

REFERENCES:

1. Babcock, E. D. "Spin-Exchange Optical Pumping with Alkali-Metal Vapors." PhD Thesis, 2005. https://old-atoms.physics.wisc.edu/papers/2005Babcock.pdf
2. Fortagh, J.; Grossmann, A.; Hansch, T.W. and Zimmermann, C. "Fast loading of a magneto-optical trap from a pulsed thermal source." Journal of Applied Physics, vol. 84, no. 12, 1998. https://doi.org/10.1063/1.369018
3. Kang, S.; Moore, K.R.; McGilligan, J.P.; Mott, R.; Mis, A.; Roper, C.; Donley, E.A. and Kitching, J. "A magneto-optic trap using a reversible, solid-state alkali-metal." Optics Letters, vol. 44, no. 12, 2019, pp. 3002-3005. https://doi.org/10.1364/OL.44.003002
4. Ha, L.C.; Noble, J.; Newell, B. and Lutwak, R. "High-Temperature Chip-Scale Atomic Clock." Journal of Physics: Conference Series, Vol. 2889 (Institute of Physics, 2024). https://iopscience.iop.org/article/10.1088/1742-6596/2889/1/012011
5. Ishikawa, K. "Vapor pressure of alkali-metal alloys in glass cells." CALPHAD: Computer Coupling of Phase Diagrams and Thermochemistry, vol. 59, 2017. http://dx.doi.org/10.1016/j.calphad.2017.08.002

KEYWORDS: Quantum sensing, magneto-optical trap, atom source, atomic clock, atom interferometer, atomic magnetometer

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