The Free-orbit Experiment with Laser Interferometry X-Rays (FELIX) belongs to a category of experiments exploring whether macroscopic systems can be in

superposition In mathematics, a linear combination or superposition is an expression constructed from a set of terms by multiplying each term by a constant and adding the results (e.g. a linear combination of ''x'' and ''y'' would be any expression of the form ...

states. It was originally proposed by the physicist

Roger Penrose Sir Roger Penrose (born 8 August 1931) is an English mathematician, mathematical physicist, Philosophy of science, philosopher of science and Nobel Prize in Physics, Nobel Laureate in Physics. He is Emeritus Rouse Ball Professor of Mathematics i ...

in his 2004 book ''

The Road to Reality ''The Road to Reality: A Complete Guide to the Laws of the Universe'' is a popular science book on modern physics by the British mathematical physicist Roger Penrose, published in 2004. It covers the basics of the Standard Model of particle ph ...

'' specifically to prove whether unconventional

decoherence Quantum decoherence is the loss of quantum coherence. It involves generally a loss of information of a system to its environment. Quantum decoherence has been studied to understand how quantum systems convert to systems that can be expla ...

processes such as gravitationally induced decoherence or spontaneous

wave-function collapse In various interpretations of quantum mechanics, wave function collapse, also called reduction of the state vector, occurs when a wave function—initially in a superposition of several eigenstates—reduces to a single eigenstate due to int ...

of a

quantum system Quantum mechanics is the fundamental physical Scientific theory, theory that describes the behavior of matter and of light; its unusual characteristics typically occur at and below the scale of atoms. Reprinted, Addison-Wesley, 1989, It is ...

occur. Later revised to take place as a tabletop experiment, if successful, it is estimated that a mass of roughly 10¹⁴ atoms would have been superposed, approximately nine orders of magnitude more massive than any superposition observed to that date (2003).

Configuration

The proposed experimental setup is basically a variation of the

Michelson interferometer The Michelson interferometer is a common configuration for optical interferometry and was invented by the American physicist Albert Abraham Michelson in 1887. Using a beam splitter, a light source is split into two arms. Each of those light be ...

but for a single photon. Additionally, one of the mirrors has to be very tiny and fixed on an isolated micromechanical-oscillator. This allows it to move when the photon is reflected on it, so that it may become superposed with the photon. The purpose is to vary the size of the mirror to investigate the effect of the mass on the time it takes for the quantum system to collapse. Originally the arms of the interferometer had to stretch into the hundreds of thousands of kilometers to achieve a photon roundtrip-time comparable to the oscillator's period, but that meant that the experiment had to take place in-orbit, reducing its viability. The revised proposal requires that the mirrors be placed into high-finesse optical cavities that will trap the photons long enough to achieve the desired delay. There are various technological challenges, but all are within high-end laboratory capabilities. The primary requirement is that the mass of the cavity remains as small as possible. To avoid noise on the interferometer and have a low probability of emitting more than one photon each time, a very low absolute temperature for the experiment is needed, on the order of 60 μK. For similar reasons, and to avoid

, the experimental device has to be in ultra-high vacuum conditions. The wavelength of the photons was calculated to be roughly 630 nm so the reflecting surfaces can be as small as possible and yet avoid refraction and reflectivity issues. The micromechanical-oscillator can be similar to the cantilevers in

atomic force microscopy Atomic force microscopy (AFM) or scanning force microscopy (SFM) is a very-high-resolution type of scanning probe microscopy (SPM), with demonstrated resolution on the order of fractions of a nanometer, more than 1000 times better than the opti ...

and the reflective surfaces typically used in similar high-demanding experiments pose no real challenge. Various elaborate electromagnetic mechanisms have been proposed to "reset" the cavities to a stable state before each repetition of the experiment.

References

{{Roger Penrose Quantum mechanics Roger Penrose

Configuration

See also

References