Quantum phase transition observed for the first time

February 2, 2017, Institute of Science and Technology Austria
Probability distribution showing the equal likelihood for the cavity being transparent and opaque at the critical point. Credit: J. Fink

A group of scientists led by Johannes Fink from the Institute of Science and Technology Austria (IST Austria) reported the first experimental observation of a first-order phase transition in a dissipative quantum system. Phase transitions include such phenomena as the freezing of water at the critical temperature of 0 degrees Celsius. However, phase transitions also occur at the quantum mechanical level, where they are still relatively unexplored by researchers.

One example of a phase transition at the quantum level is the photon-blockade breakdown, which was only discovered two years ago. During photon blockade, a photon fills a cavity in an optical system and prevents other photons from entering the same cavity until it leaves, hence blocking the flow of photons. But if the photon flux increases to a critical level, a quantum phase transition is predicted: The photon blockade breaks down, and the state of the system changes from opaque to transparent. This specific phase transition has now been experimentally observed by researchers who, for the first time, met the very specific conditions necessary to study this effect.

During a phase transition, the continuous tuning of an external parameter, for example temperature, leads to a transition between two robust steady states with different attributes. First-order are characterized by a coexistence of the two stable phases when the control parameter is within a certain range close to the critical value. The two phases form a mixed phase in which some parts have completed the transition and others have not, as in a glass containing ice water. The experimental results that Fink and his collaborators will publish in the journal Physical Review X give insight into the quantum mechanical basis of this effect in a microscopic, zero-dimensional system.

Their setup consisted of a microchip with a superconducting microwave resonator acting as the cavity and a few superconducting qubits acting as the atoms. The chip was cooled to a temperature astoundingly close to absolute zero—0.01 Kelvin—so that thermal fluctuations did not play a role. To produce a flux of photons, the researchers then sent a continuous microwave tone to the input of the resonator on the chip. On the output side, they amplified and measured the transmitted microwave flux. For certain input powers, they detected a signal flipping stochastically between zero transmission and full transmission, proving the expected coexistence of both phases had occurred. "We have observed this random switching between opaque and transparent for the first time and in agreement with theoretical predictions," says lead author Johannes Fink from IST Austria.

Potential future applications include memory storage elements and processors for quantum simulation. "Our experiment took exactly 1.6 milliseconds to complete for any given input power. The corresponding numerical simulation took a couple of days on a national supercomputer cluster. This gives an idea why these systems could be useful for quantum simulations," Fink explains.

Johannes Fink came to IST Austria in 2016 to start his working group on Quantum Integrated Devices. The main objective of his group is to advance and integrate technology for chip-based computation, communication, and sensing.

Explore further: New research explores when quantum systems get critical

More information: J. M. Fink et al, Observation of the Photon-Blockade Breakdown Phase Transition, Physical Review X (2017). DOI: 10.1103/PhysRevX.7.011012

Related Stories

Learning more about phase transitions in small systems

June 23, 2011

(PhysOrg.com) -- "People want to understand phase transitions in a finite system by quantum simulation," Luming Duan tells PhysOrg.com. Duan is a professor at the University of Michigan, located in Ann Arbor. "Being able ...

Recommended for you

ATLAS experiment observes light scattering off light

March 20, 2019

Light-by-light scattering is a very rare phenomenon in which two photons interact, producing another pair of photons. This process was among the earliest predictions of quantum electrodynamics (QED), the quantum theory of ...

How heavy elements come about in the universe

March 19, 2019

Heavy elements are produced during stellar explosion or on the surfaces of neutron stars through the capture of hydrogen nuclei (protons). This occurs at extremely high temperatures, but at relatively low energies. An international ...

Trembling aspen leaves could save future Mars rovers

March 18, 2019

Researchers at the University of Warwick have been inspired by the unique movement of trembling aspen leaves, to devise an energy harvesting mechanism that could power weather sensors in hostile environments and could even ...

Quantum sensing method measures minuscule magnetic fields

March 15, 2019

A new way of measuring atomic-scale magnetic fields with great precision, not only up and down but sideways as well, has been developed by researchers at MIT. The new tool could be useful in applications as diverse as mapping ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.