On-chip GHz time crystals with semiconductor photonic devices pave the way for new applications in physics and optoelectronics

Scientists have observed for the first time a time crystal on a microscale semiconductor chip oscillating at several billion times per second, revealing extremely high nonlinear dynamics in the GHz range.

Experimental results published in Scienceestablish a lasting connection between previously uncorrelated areas of nonlinear exciton-polariton dynamics and coherent optomechanics at GHz frequencies, say scientists from the Institute of Semiconductor Electronics. Paul-Drude (PDI) in Berlin, Germany, and from the Argentinian Institute Centro Atómico Bariloche and Instituto Balseiro (CAB-IB).

A high-quality semiconductor sample was used for the research, which acts as a trap for coherent light matter condensates.

Designed and manufactured at PDI, the sample was created by stacking one-atom-thick layers of semiconductor materials under ultrahigh vacuum conditions, ultimately creating a micron-sized “box” capable of capturing millions of quantum particles. It was then forwarded to CAB-IB for testing.

When the CAB-IB team aimed a time-independent (i.e. continuous) laser at the sample, they observed that the particles within it began to oscillate at GHz frequencies – a billion times per second.

This is the first time persistent oscillations in this range have been observed in a condensate sample on a semiconductor device.

The researchers also found that the oscillations could be fine-tuned using the optical power of the laser, with the ability to stabilize the free frequency evolution using engineered 20 GHz mechanical oscillations of the semiconductor atomic lattice.

Consistent with their theory, the researchers found that as the laser power was further increased, the particles vibrated at exactly half the mechanical vibration frequency.

“This behavior can be interpreted as different manifestations of the time crystal,” said Alexander Kuznetsov, a scientist at PDI.

“The demonstrated results add a new dimension to the physics of open many-body quantum systems, enabling frequencies several orders of magnitude higher than before and presenting new ways to control the emerging dynamics, leading to fascinating time crystals on a semiconductor platform. “

What are time crystals?

Since Nobel Prize-winning physicist Frank Wilczek first proposed his theory more than a decade ago, researchers have been searching for elusive “time crystals” – many-body systems consisting of particles and quasiparticles, such as excitons, photons and polaritons, which at their most stable the quantum state changes periodically over time.

Wilczek’s theory centered around a puzzling question: Can the most stable state of a quantum system composed of many particles be periodic in time? That is, can it exhibit temporal fluctuations characterized by beating with a precisely defined rhythm?

It was quickly demonstrated that the behavior of the time crystal cannot occur in isolated systems (systems that do not exchange energy with the surrounding environment). However, this disturbing question did not end the topic, but motivated scientists to look for the conditions under which such time crystal behavior could develop in an open system (i.e. one that exchanges energy with its surroundings).

And although time crystals have been observed several times in out-of-equilibrium systems, much about them remains undetermined: their internal dynamics are largely beyond scientists’ current understanding, and their potential applications remain in the realm of theory rather than practice.

“This work represents a paradigmatic shift in the approach to time crystals, offering the possibility of extending such studies to arbitrarily large arrays (grids) of localized time crystals to study their interactions and synchronization,” said Alejandro Fainstein, a senior researcher and professor who led the CAB- team IB.

“Thanks to it, we were able to discover the special behaviors of quantum materials. Since the materials used are semiconductors compatible with integrated photonic devices, and the displayed frequencies are relevant to both classical and quantum information technologies, we anticipate additional steps in which we will try to control these behaviors for applications including photon-to-RF conversion at quantum.

Potential applications

According to the research team, this experiment is promising for the use of time crystals in integrated and microwave photonics.

“Thanks to polariton-enhanced coupling between GHz phonons and near-infrared photons, the results have the potential to be applied to (quantum) microwave and optical frequency conversion,” said Paulo Ventura Santos, senior scientist at PDI.

Semiconductor-based nonlinear optoelectronic systems – devices that can convert light energy into electrical energy or vice versa – are attracting particular attention due to their potential applications in chip photonics. However, their study is extremely difficult due to the multi-body complexes (such as time crystals) that determine their electronic and optical properties.

“A deeper understanding of well-defined regimes in these many-body systems, such as those that the PDI/CAB-IB team helped identify, could help elucidate these internal dynamics and, in turn, help develop methods for controlling and exploiting such systems for applications ” – said Gonzalo Usaj, theory leader in the CAB-IB team.

Provided by Paul-Drude-Institut für Festkörperelektronik