Quantum Friction
The first direct experimental measurement of friction between solid materials at the quantum level has purportedly been made by a group of Chinese scientists in a historic breakthrough. This surprising discovery was made by researchers at the Lanzhou Institute of Chemical Physics while working with ultra-thin graphene sheets. It could mark the beginning of a new era in the construction of low-power nanodevices and the management of friction in sophisticated quantum materials. This month, the journal Communications published their findings.
From the way tires grip the road to the wear and tear on mechanical components, friction is a force that permeates everything. The prevailing belief for centuries was that friction was caused by the rubbing of rough surfaces, where tiny bumps and sticky areas prevent motion and turn energy into heat. On the other hand, quantum friction a distinct and more mysterious phenomenon occurs at the quantum scale. This special drag force, which is totally quantum computing and is mediated by the fluctuations of the material-modified quantum electrodynamic vacuum, happens even when objects move in relation to one another in a vacuum.
The Chinese team’s finding was especially unexpected: they discovered that when the graphene material thickened, friction did not rise; rather, some of the thicker folds slid more smoothly. They explained this intriguing phenomenon by pointing out that bending the graphene sheets changed the way electrons moved within the substance, locking them into fixed energy levels and making it more difficult for motion to be transformed into heat. In addition to confirming the existence of quantum friction, this “revelation was a bonus” for the researchers because it provided insight into how it might be used to create incredibly efficient quantum machines and tiny electronics that seldom wear out.
Quantum friction has been a difficult topic for physicists to explore for decades, mostly limited to theoretical research. This drag force, which is known as quantum friction at zero temperature, is experienced by two or more objects moving in relation to one another in a vacuum. The fundamental characteristics of the quantum vacuum a theory in which even empty space is seething with fluctuating electromagnetic fields are the basis for this contactless, non-conservative interaction.
A long-standing issue in contemporary physics is the interaction of an atom with its electromagnetic surroundings, which involves intricate interactions between solid-state physics, quantum electrodynamics, atomic physics, and statistical physics. A Doppler-shifted frequency changes how an atom interacts with the electromagnetic field when it travels parallel to a material surface, which is essential for quantum friction to happen.
A force component parallel to the surface that resists motion is believed to develop due of the material’s dissipative and dispersive qualities, which induce a little delay in the “image dipole” formed underneath the surface as the atom moves. Quantum friction is regarded as a “low-frequency, off-resonant phenomenon,” highlighting the material’s dissipative qualities, at low and moderate velocities.
With multiple predictions for its scaling principles, the theoretical understanding of quantum friction is complicated. The frictional acceleration can be cubic in velocity and very sensitive to the atom-surface separation for a single atom travelling at non-relativistic speeds parallel to a flat surface of an Ohmic material. It also decreases noticeably with increasing distance. For example, the force may be reduced by 20 to 30 orders of magnitude if an atom were moved from a surface from 1 nanometre to a few hundred nanometres away.
Because of its high sensitivity, which frequently falls below the sensitivity of existing detectors, direct experimental detection has proven to be extremely difficult. Even the viability of ever measuring it has been questioned by certain writers.
Recent theoretical research, such that described in APL Photonics, indicates that there are a number of ways to greatly increase the quantum frictional force. These consist of:
- Making use of the material’s spatial dispersion: Different materials have different dissipative channels; for example, semiconductors such as n-doped silicon or Germanium can have stronger low-frequency damping mechanisms than conductors, which results in higher friction. Landau damping, which greatly increases the force, can also result from the mean free path of electrons in a conductor.
- Selecting geometries that inhibit net angular momentum transfer: This may lower the total frictional force by incorporating a “quantum rolling friction” component, in which angular momentum is transported in a “counterintuitive” way. To lessen this, certain geometries can be created.
- Making use of the force’s non-additive characteristics: Quantum friction behaves strongly non-additivistically with geometry, in contrast to equilibrium forces. For instance, the force can be increased by 14–56 times when cavities (parallel plates) or waveguides are used in place of single planar interfaces.
These theoretical findings provide “modest optimism that quantum friction might become experimentally accessible in the near future” by proposing an enhancement factor comparison to the most basic estimations.
To get around these obstacles, experimental techniques like atom interferometry which uses cold atoms or atomic beams diffracted at grating and detection through nitrogen-vacancy (NV) centres in nano-diamonds are being investigated. Notably, conditions favourable to seeing quantum friction might be created by bringing NV-centers within a few nanometres from a high-frequency rotating surface, achieving relative velocities up to a few km/s.
The quest for direct observation of quantum friction is similar to the difficulties in verifying other fluctuation-induced phenomena such as the Casimir force and London dispersion forces in the past. Decades after their prediction, they were finally measured with clarity, which made them relevant in a variety of nanotechnological devices.
Some view the search for quantum friction as a means of obtaining direct experimental access to the “conceptual core of nonequilibrium quantum field theory,” which would open up new horizons in theoretical and experimental physics beyond the immediate objective of verifying the force. Therefore, the recent discovery of graphene represents a major advancement in this continuing scientific endeavor.
