Ground State Cooling of a Levitated Nanoobject for Precision Tests of the Standard Model at Micron Scales

The goal of this PhD project is to optically levitate and cool to the center of mass (COM) motional ground state a nano-meter sized dielectric object (silica spheres, nano diamonds). We seek to realize it in a way suitable for precision measurements of short-range forces.

Tests of deviations from Newtonian gravity law at sub-micron ranges due to possible new forces or extra space dimensions, characterization of the fully Quantum mechanical Casimir-Polder forces, bounds on matter neutrality and other fundamental physics tests can be realized with optically levitated nanoobjects [1].

While close to ground state cooling of levitated nanospheres has been shown using cavity coupled nanospheres [2] as well as charged nanospheres [3] in a single beam optical trap, both methods are inherently difficult to combine with a precision force measurement close to a surface (sub-micron distance) due to low reflectivities of metallic mirrors and orders of magnitude larger Coulomb force respectively.

In our newly designed ultra-stable, cryogenic UHV chamber we plan to implement a single beam optical or a standing wave optical trap to overcome these limitations.

The experiment consists of several independent challenging projects, which will teach the PhD candidate a great deal in quantum mechanics, laser physics, vacuum and cryo-technology, optical design and many other theoretical and experimental skills.

[1] “Searching for new physics using optically levitated sensors”, David C. Moore and Andrew A. Geraci, Quantum Sci. Technol. 6 (2021)
[2] “Searching for new physics using optically levitated sensors”, U. Delic et al. Science (2020)
[3] “Real-time optimal quantum control of mechanical motion at room temperature”, Lorenzo Magrini et al., Nature 595, (2021)

If interested, please contact Prof. Andrew Geraci at andrew.geraci@northwestern.edu

Matter Wave Interference with Nanospheres

The largest objects, which have been shown to interfere are molecules with masses of up to 25kDa [1]. The goal of this PhD project is to demonstrate directly matter-wave interference with optically levitated nanoobjects (R = 10-100nm) [2], which are more than four orders of magnitude larger. This would not only test the fundamentals of Quantum mechanics, but also put limits on possible decoherence mechanisms and wave function collapse models, contributing to one of the most intriguing problems of modern physics, the Measurement Problem.

To achieve this ambitious goal many experimental challenges, must be overcome. To reduce collisional decoherence, pressures of ≈1⋅10^-15torr need to be achieved. Absorption and emission of thermal radiation need to be suppressed to cryogenic levels using a cryogenic vacuum chamber and possibly actively cooling the particle using Anti-Stokes-cooling schemes, pointing stability at long- and short-time scales of only few nanometers and many others. This together with fascinating quantum mechanical calculations and optical designs give a unique opportunity for the PhD student to become an expert in many crucial AMO skills and develop own ideas.

[1] “Quantum Superpositions of Molecules beyond 25kDa”, Yaakov Y. Fein et al., Nature Physics Vol. 15 (2019)
[2] “Sensing short range forces with a nanosphere matter-wave interferometer”, Andrew Geraci and Hart Goldman, Physical Review D (2015)

If interested, please contact Prof. Andrew Geraci at andrew.geraci@northwestern.edu and Dr. Alexey Grinin at alexey.grinin@northwestern.edu