Onofrio Research Group

(For an enjoyable description the Casimir effect including a history of Casimir research, check out Astrid Lambrecht's PhysicsWeb article.)

Classical vacuum is a physical concept first studied by ancient Greek philosophers like Aristotle and Democritos, especially with respect to the debate between idealistic and materialistic approaches to natural philosophy. In more recent times, the structure of classical vacuum was demonstrated by Evangelista Torricelli and Otto von Guericke through experiments which have been seminal in creating modern vacuum technology.
However, we know that classical physics, as a fundamental physical theory, is unable to consistently explain phenomena at the atomic and subatomic level, and it has been superseded by a more complete theory called quantum mechanics. In quantum mechanics, it is relatively simple to infer that vacuum is not empty, but instead always contains irreducible energy and momentum fluctuations. These fluctuations can also be manifested at the macroscopic level for instance through the Casimir force, proposed in 1948 by theoretical physicist Hendrik Casimir.

PI
Roberto Onofrio

Graduate Students
Michael Brown-Hayes
Woo-Joong (Andy) Kim
Qun Wei

Undergraduate Students
Jonathan Huang
Scott Middleman
Nathan Monnig
Taylor Smith

Ultracold Atoms

Casimir Effect
Static Casimir Effect
Dynamic Casimir Effect

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Static Casimir apparatus, with microscope in foreground, fiber and electrical feedthroughs on the left side, pump connection and electrical feedthroughs on the right, and coarse approach micrometers on top and bottom.

Static Casimir Effect: One of the open problems in the physics of Casimir effects is the interplay between quantum vacuum fluctuations and thermal contributions. We argue that this problem can be solved by measuring the Casimir force in a cylinder-plane geometry. Preliminary tests with a prototype system developed at Dartmouth suggests that the Casimir force could be measured in the 1-3 micrometer range with sufficient precision to distinguish between controversial predictions for the thermal corrections.
	Above: closeup of static Casimir apparatus, showing optical fiber/holder, resonator, and cylinder/holder. PZTs provide fine approach/parallelization of cylinder and feedback loop for the optical fiber. Left: laser, collimation system, and signal mixer. The laser signal reflected off the resonator allows for FFT and closed-loop optimization of the system sensitivity.
The control of the thermal corrections is also crucial to look for Yukawian forces with gravitational coupling strength expected according to various unification models in the 1-100 micron range. A dedicated torsion balance to measure the Casimir force is under development at the Institute Laue-Langevin in Grenoble, in the framework of a Dartmouth-Grenoble-Paris collaboration.

Dynamic Casimir Effect:
Motion in quantum vacuum is predicted to be dissipative in nature for non-uniformly accelerated bodies. This important effect, named the dynamical Casimir effect, with potentially profound implications even for Newton's Principia, implies that there will be a parametric generation of photons from quantum vacuum whenever boundaries are in non-uniformly accelerated motion. The effect is enhanced in a high-finesse cavity, as photons can build up exponentially, but it still remains at the limit of reach of today's experimental techniques. We have proposed to develop a generation scheme based upon the convergence of nanotechnology and cold atom spectroscopy. The first feasibility studies of this difficult, long term project are underway in our laboratory at Dartmouth, in particular in the direction of exploiting Rydberg atoms in super-radiant states.

Department of Physics and Astronomy, Dartmouth College