Solid-State Emitters Now Boast Linewidths Approaching Their Lifetime Limit

Scientists at the Department of Physics, in collaboration with University at Buffalo SUNY, have demonstrated a new method for mitigating spectral diffusion in quantum systems. Kilian Unterguggenberger and colleagues report the first experimental observation of this mitigation, accomplished by driving a solid-state emitter with a periodic sequence of optical pi-pulses. The technique effectively shifts the emission and absorption maximum, reducing the inhomogeneously broadened optical linewidth to near its lifetime limit and concentrating approximately half of the absorption onto a user-defined target frequency. This all-optical control offers a vital pathway towards engineering the properties of single photon emitters for diverse quantum technologies, as it relies solely on coherent quantum evolution and is applicable to both individual and ensembles of emitters. All-optical pi-pulse sequences achieve unprecedented narrowing of solid-state emitter linewidths The inhomogeneously broadened optical linewidth of a solid-state emitter was reduced to just 27MHz, representing a narrowing to twice the lifetime limit of 12.9MHz. Prior to this work, linewidths were significantly broader, reaching 104MHz and presenting a substantial hindrance to precision in quantum applications. This substantial reduction, achieved through an entirely optical technique, circumvents the limitations imposed by static fields or complex feedback loops, offering a novel and potentially more scalable method for spectral control. Solid-state emitters, while promising for quantum technologies, often suffer from inhomogeneous broadening due to variations in their local environments. These variations lead to a distribution of emission energies, broadening the overall spectral linewidth and reducing the efficiency of single-photon emission. By manipulating the emitter with a periodic sequence of optical pi-pulses, scientists were able to concentrate approximately half of the absorption onto a freely selectable target frequency, demonstrating unprecedented control over light emission and a significant step towards overcoming this broadening effect. The ability to precisely define the emission frequency is crucial for applications requiring spectral purity, such as quantum key distribution and resonant interactions with other quantum systems. Photoluminescence excitation spectroscopy revealed a nearly symmetric array of dips, indicative of stimulated emission and a refocusing of spectral weight. These dips arise from constructive interference of the emitted photons, confirming that the pi-pulse sequence is effectively manipulating the emitter’s quantum state. Altering the delay between these pulses, down to 5.8 nanoseconds, changed the spacing of these dips, confirming theoretical predictions regarding their relationship to the pulse timing. This precise control over the dip spacing provides further evidence of the coherent nature of the spectral manipulation. Even with deliberately detuned pulse carrier frequencies, shifting the emission up to eight natural linewidths, a discernible dip remained at the target frequency, demonstrating the robustness of the technique and its ability to function even under non-ideal conditions. This is particularly important for practical applications where perfect frequency alignment may be difficult to achieve. Precise spectral shaping is paramount for advancing single-photon sources used in quantum technologies, enabling more reliable performance in areas like secure communication and quantum computing. A solid-state emitter, specifically a nitrogen-vacancy (NV) centre in diamond, underwent this all-optical spectral control, allowing for potential scalability in quantum networks and photonic quantum computing due to the emitter’s compatibility with photonic integration. NV centres possess unique properties, including a relatively long coherence time and bright emission, making them attractive candidates for quantum information processing. Unlike alternative methods for mitigating spectral diffusion, a common issue in solid-state emitters, this approach circumvents the need for external static fields or feedback loops, simplifying the experimental setup and reducing potential sources of noise. The technique’s success with the NV centre suggests a pathway towards creating durable and scalable quantum systems, as diamond is a robust material that can withstand harsh environmental conditions. Coherent spectral control via pulsed excitation of a diamond nitrogen-vacancy centre Optical pi-pulses, precisely timed bursts of light that flip a quantum system’s state, formed the cornerstone of this work. These pulses, applied in a repeating sequence, are akin to carefully timed pushes on a swing to maximise its height. In the context of the NV centre, a pi-pulse rotates the electron spin from one state to another, effectively swapping the roles of the ground and excited states. This technique was utilised to manipulate the emission from a solid-state emitter, effectively shifting its spectral output by exploiting the principles of coherent quantum evolution. Coherent evolution refers to the deterministic evolution of a quantum system governed by the Schrödinger equation, without the introduction of decoherence or randomness. The method hinges on applying these pulses during the excited state lifetime of the emitter, a fleeting moment vital for controlling its behaviour. The excited state lifetime of the NV centre is approximately 12.9MHz, meaning the emitter returns to its ground state within approximately 78 nanoseconds. Applying the pi-pulses within this timeframe allows for precise manipulation of the quantum state before decoherence sets in. Narrowing light emission with light unlocks partial spectral control of quantum emitters Advances in quantum technologies, particularly building dependable single-photon sources, require controlling the colour of light emitted by solid materials. While this work demonstrates a sharp narrowing of emitted light using only light itself, achieving complete absorption concentration remains elusive. Currently, the team focuses approximately half of the absorption onto the desired frequency. This limitation hints at underlying complexities in manipulating quantum systems, potentially requiring more sophisticated pulse sequences or alternative emitter designs. The incomplete absorption concentration may be due to factors such as imperfect pulse shaping, decoherence during the pulse sequence, or the presence of multiple emitters with slightly different energies. Further investigation is needed to fully understand the limitations of the technique. Further research will explore methods to enhance the efficiency of this process, potentially through optimisation of pulse shapes or the incorporation of additional control parameters. For example, using shaped pulses with tailored spectral profiles could further refine the emission characteristics. Employing a repeating sequence of precisely timed light pulses offers a new method for controlling the colour of light emitted by solid-state quantum emitters. These pulses manipulate the quantum state of the material, shifting its emission characteristics without needing external static fields, and enhancing potential for stable single-photon sources. This all-optical technique represents a major step forward in quantum technology, paving the way for more compact and efficient quantum devices and offering a promising route towards realising practical quantum networks and computers. The researchers successfully demonstrated a method for narrowing the emitted light from a solid-state quantum emitter using a series of optical pi-pulses. This control is achieved by concentrating approximately half of the absorption onto a freely selectable target frequency, mitigating spectral diffusion and reducing the optical linewidth close to the lifetime limit. The technique relies solely on manipulating the quantum state with light, making it potentially applicable to various quantum emitters. Further work aims to optimise pulse shapes to improve the efficiency of this spectral control. 👉 More information 🗞 Spectral Diffusion Mitigation with a Laser Pulse Sequence 🧠 ArXiv: https://arxiv.org/abs/2604.21659 Tags: