CAREER: Matter-Wave Quantum Optics in Spin-Space in Ultracold Sodium Gases

University Of Oklahoma Norman Campus, Norman OK

Investigators

Abstract

This project is jointly funded by the Atomic, Molecular, and Optical Physics Experiment Program, and the Established Program to Stimulate Competitive Research (EPSCoR). Collisions between atoms in gases happen all around us, for example in the air that we breathe every day. At room temperature, the collisions are random and very difficult to control. By cooling a gas to ultracold temperatures near absolute zero (below minus 273 degrees Celsius) and trapping it in the center of a vacuum chamber, collisions can be controlled and used to develop new technologies such as quantum-limited sensors for impurities. An ultracold gas behaves like a single quantum mechanical object, a matter wave. Collisions still take place in the matter wave, but they now happen in a predictable fashion. In a sodium matter wave, the collisions can be controlled precisely via microwave radiation. The colliding atoms behave like small magnets with magnetic north and south poles determined by the direction of their atomic spin. During collisions, atoms experience each other's magnetic fields and change their spin directions. As they change directions, the atomic spins become correlated with each other at the quantum level, a phenomenon known as quantum entanglement. Quantum entanglement is useful when atoms are used as sensors. All entangled atoms react to external influences in unison, increasing the sensitivity of a sensor. This research project will use controlled collisions in sodium matter waves to study quantum-enhanced sensing and other quantum technologies. This project will study the role of impurities and will also explore differences and similarities compared to experiments with entangled beams of light. The research will improve our experimental understanding of quantum technologies based on matter waves under realistic conditions, in the presence of loss and impurities. This has practical applications for development of robust quantum-enhanced sensors, for development of quantum-enhanced probes for ultracold gases, and for improving our understanding of how we can control spin in matter waves at the quantum level. The goal of this research program is to study a new generation of quantum technologies based on quantum engineering of matter-waves, such as quantum-enhanced sensors for external fields with high spatial resolution, quantum-enhanced probes of ultracold atomic samples to measure spin populations with reduced noise, and quantum-enhanced matter-wave devices such as phase-sensitive amplifiers, similar to those known from quantum optics with light. The control of matter-waves is exerted by microwave-dressing and RF control of spin-exchange collisions in a Bose-Einstein condensate of atomic sodium in the limit of long evolution times. During spin-exchange collisions in the F=1 sodium gas, pairs of atoms with magnetic quantum number m=0 collide and change into pairs with m=+/-1 and vice versa. This process generates quantum entanglement similar to four-wave mixing with light. But there are important differences in the atomic system due to extra terms in the Hamiltonian not present in the photonic system. These differences become increasingly important for long evolution times, t>|h/c|, where t>30 ms in a sodium Bose-Einstein condensate and c is the spin-exchange collisional energy. They give rise to quantum phase transitions that can generate massive entanglement. The ground state depends uniquely on whether the gas is antiferromagnetic (c>0, Na), where it is massively entangled, or ferromagnetic (c<0, Rb), where it is not entangled. The goal of this project is to make use of the unique features of ultracold sodium, and recent technological advances in matter-wave quantum optics, to demonstrate a robust and future-proof platform for matter-wave quantum technologies that will lay the groundwork for extensive long-term research on matter-wave devices similar to photonic devices. This is done by studying the following quantum technologies: a) quantum-enhanced sensing via spin-mixing interferometry in the long evolution time limit, b) quantum-enhanced probing of spin populations, c) quantum state synthesis of exotic many body states, and d) quantum simulation of the effect of impurities. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.