GHz on-chip timing crystals with semiconductor photonics pave the way to new optoelectronic physics and applications

Researchers have for the first time observed a timing crystal on a small-scale semiconductor chip oscillating at a rate of several billion times per second, revealing extremely high nonlinear dynamics in the GHz range.

The results of the experiment, published in scienceestablish a strong link between the once uncorrelated areas of nonlinear exciton-polariton dynamics and coherent optomechanics at GHz frequencies, say researchers from the Paul-Drude-Institute for Solid State Electronics (PDI) in Berlin, Germany and based in Argentina. Centro Atómico Bariloche and Instituto Balseiro (CAB-IB).

The research was carried out using a high-quality semiconductor-based sample that acts as a trap for coherent condensates of light matter.

Designed and fabricated at PDI, the sample was created by depositing one-atom-thick layers of semiconductor materials under extremely high vacuum conditions, ultimately forming a micron-sized “box” with the ability to trap millions of quantum particles. It was then transferred to CAB-IB for testing.

When the CAB-IB team pointed a time-independent (ie continuous) laser at the sample, they noticed that the particles it contained began to oscillate at GHz frequencies – a billion times per second.

This is the first time that stable oscillations in this range have been observed in a condensation sample in a semiconductor device.

The researchers also found that the oscillations can be well tuned by the optical power of the laser, with the possibility to stabilize the free frequency evolution of the engineered 20-GHz mechanical vibrations 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 frequency of mechanical vibrations.

“This behavior can be interpreted as different manifestations of a 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 introducing new ways to control the evolving dynamics, which leads to fascinating time crystals on a semiconductor platform.”

What are time crystals?

Ever since Nobel Prize-winning physicist Frank Wilczek first proposed his theory more than a decade ago, researchers have been searching for the elusive “time crystals”—many-body systems made up of particles and quasi particles such as excitons, photons, and polaritons that, in their most stable quantum state, change periodically in time.

Wilczek’s theory centered around a puzzling question: Can the most stable state of a many-particle quantum system be periodic in time? That is, can it exhibit temporal oscillations characterized by a beat with a well-defined rhythm?

It was quickly shown that time crystal behavior cannot occur in isolated systems (systems that do not exchange energy with the surrounding environment). But far from closing the subject, this vexing question motivated scientists to look for the conditions under which an open system (that is, one that exchanges energy with the environment) can develop such crystalline behavior.

And while time crystals have now been observed in a few cases in systems taken out of equilibrium, much about them remains undefined: their internal dynamics are largely beyond the current understanding of scientists, and their potential uses have remained in the realm of theory and not in practice. .

“This work represents a paradigm shift in the approach to time crystals, providing an opportunity to extend such studies to arbitrary arrays (lattices) of localized time crystals to study their interactions and synchronization,” said Alejandro Fainstein, researcher senior and professor who led the CAB-IB team.

“Through it, we have been able to discover special behaviors of quantum materials. Because the materials involved are semiconductors compatible with integrated photonic devices, and the frequencies displayed are relevant to both classical and quantum technologies. information, we envision additional stages in which you will try to control these behaviors for applications, including photon-to-radio-frequency conversion at the quantum level.”

Possible applications

According to the research team, this experiment shows promise for using time crystals in integrated and microwave photonics.

“Due to the enhanced polarity coupling between GHz phonons and near-infrared photons, the results have the potential for applications in (quantum) conversion between microwave and optical frequencies,” said Paulo Ventura Santos, a 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 for their potential applications in on-chip photonics. But they are extremely difficult to study because of the many-body complexes (such as time crystals) that determine their electronic and optical properties.

“A deeper understanding of the well-defined regimes within these multi-body systems, such as those the PDI/CAB-IB team helped to identify, can help elucidate these internal dynamics—and in turn help in developing methods to control and exploit such systems for applications,” said Gonzalo Usaj, head of theory from the CAB-IB team.