Scientists ‘freeze’ mild right into a supersolid utilizing ‘quantum theatre’

Gentle at all times travels at 3 lakh km per second in a vacuum. It can’t be trapped and solidified as a result of the particles of sunshine, photons, don’t have any relaxation mass and don’t work together strongly with one another. Typically, mild exists solely as a particle or wave. However lately, a crew of researchers from Italy’s College of Pavia and CNR Nanotec reported efficiently ‘freezing’ mild by manipulating photons in a meticulously organized ultra-cold atmosphere.

This groundbreaking analysis exhibits mild may be was a supersolid and that it may stream with nearly zero viscosity. The findings have been revealed in Nature.

Slowing mild

A supersolid is an unique section of matter during which particles are organized in a crystalline construction but additionally transfer like a non-viscous fluid. In different phrases, it combines the friction-free stream of a superfluid with the ordered construction of a crystalline strong. Normally solids don’t transfer on their very own, however supersolids change route and density relying on their particles’ interactions whereas sustaining an organised inner construction.

Physicists predicted the thought of a supersolid within the Nineteen Sixties and first created it in a laboratory in 2017. In a precursor, the Danish physicist Lene Hau and her crew used a Bose-Einstein condensate — one other unique state of matter — of ultra-cold atoms to sluggish a beam of sunshine to 17 m/s in 1999. Two years later, the crew managed to fully ‘cease’ a light-weight pulse. They achieved this feat by ‘transporting’ details about the sunshine to the atoms within the condensate. This technically froze the sunshine, which might be ‘launched’ from the atoms as wanted.

These research confirmed mild might be saved as an ‘excitation’ in matter. However this system solely used matter to briefly retailer the sunshine quite than turning the sunshine right into a strong construction.

In 2010, a gaggle in Germany created a Bose-Einstein condensate composed purely of photons by confining mild in a dye-filled optical microcavity. This allowed photons to kind a coherent quantum state, basically liquid mild, nevertheless it nonetheless wasn’t a strong construction.

Polaritons within the combine

The brand new research marks the primary time scientists have managed to couple mild with matter to create a supersolid. The feat opens up new prospects in condensed matter physics, the sector that gave us optical fibres, lasers, semiconductors, and quantum computing.

Solids and liquids are two frequent phases of matter. Solids flip into liquids when they’re heated and liquids flip to solids when they’re cooled. There are additionally sure quantum states of matter that flip into one another in peculiar methods.

The brand new analysis used a quantum mechanical method that relied on the properties of polaritons. These are hybrid particles that behave generally like mild and generally like matter. They’re created by coupling photons with packets of vitality inside supplies, like phonons (vibrational vitality) or excitons (electron-hole pairs).

The researchers used an aluminium gallium arsenide semiconductor platform as a waveguide — a channel by way of which waves can cross — match with a supply of excitons and a laser. The waveguide had a microscopic construction with a periodic grating. The etched ridges influenced the polaritons’ movement, trapping them in a daily sample. The crew used a pulsed laser to keep up a dense polariton condensate at a temperature of about –269º C.

‘Quantum theatre’

When the laser mild entered the semiconductor, polaritons have been created after which confined by the grating. They subsequently settled right into a periodic lattice of hybrid light-matter waves, leading to a density modulation comparable to a crystal-like construction. This low-loss situation allowed the polaritons to outlive lengthy sufficient to organise themselves specifically methods. These polaritons have been discovered to behave like a supersolid.

This was a state of sunshine quite than matter: a polariton condensate exhibiting a crystalline construction and superfluid coherence. The polaritons have been organised right into a periodic sample in area, identical to how carbon atoms are organised in a diamond or silicon dioxide molecules are organized in a quartz crystal.

The researchers used quantitative strategies to substantiate the state’s supersolid character. For instance, they discovered the system might decrease its vitality by spontaneously producing a density wave and ‘freezing’ into an ordered sample whereas sustaining a single, coherent quantum state, making it a quintessential supersolid.

In a Nature briefing, the researchers described this phenomenon as “quantum theatre”. Think about sitting in a packed auditorium with solely three seats left, all within the first row. Everybody desires the centre seat as a result of they need the perfect view, however it may accommodate just one individual. In a “quantum theatre”, all bosonic particles — I.e. force-carrying particles — can concurrently occupy the center seat. Once they do, a Bose-Einstein condensate is shaped.

(I.e. the bosons in an remoted quantum system are all allowed to have the identical vitality on the identical time. A Bose-Einstein condensate is shaped once they do. Matter-making particles, or fermions, in a system can’t have the identical vitality on the identical time, nevertheless. That is known as Pauli’s exclusion precept. That is what creates the totally different parts within the periodic desk.)

Potential functions

This stated, interactions between particles additionally restrict the quantity that may occupy that one seat. Past some extent, pairs of particles get pushed to the seats on the left and proper. In order particles gather within the quantum theatre, two “satellite tv for pc condensates” take form on both aspect of the central one. This fashion, a supersolid state emerges from the condensate.

The experiment demonstrated that mild can exhibit sure states of matter in the best — if additionally laboratory-engineered — situations. The opportunity of turning mild right into a quantum construction might render photonic supersolids extra accessible for experimentation and potential functions akin to lossless optical vitality transport and optical computing parts.

Shamim Haque Mondal is a researcher within the Physics Division, State Forensic Science Laboratory, Kolkata.

Printed – June 29, 2025 06:30 am IST