Researchers at the Paul-Drude-Institute for Solid State Electronics (PDI) have discovered a novel modulation regime in a semiconductor-based laser, characterized by the emergence of “acceleration beats.” This regime allows for the coherent manipulation of quantum systems using modulation periods longer than the coherence time, provided that the modulation amplitude is large enough.
Harmonic modulation of light sources, such as lasers, is crucial for many modern and emerging telecommunications technologies. Traditionally, two regimes of modulation are known: the adiabatic regime and the non-adiabatic regime. In the adiabatic regime, the coherence of light dissipates faster than the modulation cycle, while in the non-adiabatic regime, several modulation cycles fit within the system’s coherence time. However, controlling modulations requires a delicate balance, as the greater the shaking (modulation amplitude), the faster the system loses its coherence.
In this new regime, the PDI team demonstrated what happens when a laser-like opto-electronic resonance is modulated with extreme modulation amplitudes, revealing a novel aspect of such modulation caused by the acceleration. The modulation is neither adiabatic nor non-adiabatic but a fundamentally different regime.
The researchers introduced high-amplitude harmonic modulation to the emission energy of a semiconductor-based, micron-sized coherent light source. They observed the emergence of “acceleration beats”—spectral oscillations related to varying rates of energy change (i.e., the acceleration) of the source rather than to the velocity of energy changes, as is the case for most physical systems under low-amplitude perturbation.
The observed effect is universal and could be observed in any kind of system under harmonic modulation. This is the first known experimental demonstration of the acceleration beats, owing to the ability to rapidly modulate a solid-state system with large-enough amplitude. The beats could have already been predicted using existing models.
The study opens new possibilities to produce high-frequency spectral features using much lower modulation frequency and to develop new protocols for the control of quantum systems. The fundamental character of the discovery raises questions about whether acceleration beats can be observed under other extreme conditions in cosmic phenomena and in high-energy particles.
The experiment’s design involved a semiconductor microcavity, a box made of layered semiconductor materials, and piezoelectrically generated acoustic waves that could modulate the energy of the condensate with amplitudes that exceed by up to two orders of magnitude the modulation quantum.
More information about this study can be found in the article ‘Acceleration beats’ shine bright light on a novel universal modulation regime in a semiconductor-based laser, published in Nature Communications.
