Fabrication and Spectroscopy of 229ThF4 Thin Films for Solid-State Nuclear Clocks

Główne pojęcia

The 229Th nuclear isomeric transition can be driven and observed in 229ThF4 thin films, opening up new possibilities for integrated and field-deployable solid-state nuclear clocks with reduced radioactivity.

Streszczenie

The authors demonstrate the fabrication of 229ThF4 thin films using a miniaturized physical vapor deposition (PVD) process, consuming only micrograms of 229Th material. They observe the 229Th nuclear isomeric transition in these thin films through laser spectroscopy, with the measured lifetimes being significantly shorter than in previously studied 229Th-doped crystals.

The authors perform density functional theory (DFT) calculations on the monoclinic ThF4 crystal structure, which reveals two non-equivalent 229Th sites with distinct electric field gradients. This provides the opportunity to independently probe two separate populations of 229Th nuclei, potentially improving the performance of a 229ThF4-based nuclear clock.

The authors estimate the performance of a 229ThF4 nuclear clock, predicting a fractional instability of 5 × 10−17 at 1 second, comparable to state-of-the-art optical atomic clocks. The 229ThF4 thin films are also promising for studying Purcell effects and nuclear superradiance due to the high emitter density.

Overall, this work demonstrates a scalable solution to the challenges of material availability and radioactivity limits in solid-state nuclear clock development, paving the way for integrated and field-deployable nuclear clock devices.

Statystyki

"The measured lifetimes in these samples, 150(15)stat(5)sys s on Al2O3 and 153(9)stat(7)sys s on MgF2, are substantially shorter than that observed in 229Th:CaF2 (τ = 641(4) s [3]) and 229Th:LiSrAlF6 (τ = 568(13)stat(20)sys s [2]) crystals."
"Assuming a 100 nm thick film, a probe laser linewidth significantly smaller than the inhomogeneous Zeeman-limited transition linewidth, and probe laser power of 1 µW, the performance of a clock based on the |5/2, ±1/2⟩↔|3/2, ∓1/2⟩ transition is estimated to have a fractional instability of 5 × 10−17 at 1 s for both Type 1 and Type 2 sites."

Cytaty

"The demonstrated fabrication of 229ThF4 thin film targets with thicknesses 30–100 nm and diameter 50 µm–5 mm and the ensuing observation of the nuclear clock transition therein clearly show a pathway towards a future integrated low-radioactivity solid-state nuclear clock that can be fabricated with existing thin film coating technology."
"The emitter density in 229ThF4 (λ/nThF4)3ρTh > 106 is more than 3 orders of magnitude higher than that achieved in 229Th-doped crystals. Using 229ThF4 waveguides or resonantors for increased optical density, a new regime for quantum optics studies involving nuclear superradiance and coherent nuclear forward scattering appears accessible in 229ThF4."

Kluczowe wnioski z

$^{229}\mathrm{ThF}_4$ thin films for solid-state nuclear clocks

by Chuankun Zha... o arxiv.org 10-03-2024

https://arxiv.org/pdf/2410.01753.pdf

Głębsze pytania

How can the crystallinity and microstructure of the 229ThF4 thin films be further improved to enhance the participation fraction of the nuclear transition and reduce inhomogeneous broadening?

To enhance the crystallinity and microstructure of the 229ThF4 thin films, several strategies can be employed. First, optimizing the physical vapor deposition (PVD) parameters, such as substrate temperature, deposition rate, and ambient pressure, can lead to improved film quality. Higher substrate temperatures may promote better crystallization and reduce defects, while a controlled deposition rate can help achieve a more uniform film thickness, minimizing inhomogeneities.
Second, post-deposition treatments such as annealing in a controlled atmosphere could be beneficial. Annealing can help relieve internal stresses and promote grain growth, leading to a more crystalline structure. Additionally, introducing a fluorination process post-deposition may enhance the film's microstructure by improving the stoichiometry and reducing carbon and oxygen contamination, which can act as quenching centers.
Third, utilizing single crystal substrates for the deposition process can provide a better lattice match and facilitate the growth of more ordered films. This approach can help align the crystal structure of the 229ThF4 thin films with the substrate, potentially leading to improved crystallinity and reduced inhomogeneous broadening.
Finally, exploring the use of advanced fabrication techniques such as molecular beam epitaxy (MBE) or atomic layer deposition (ALD) could allow for more precise control over the film's microstructure, leading to enhanced participation fractions of the nuclear transition and reduced inhomogeneous broadening.

What other host materials besides ThF4 could be explored for 229Th doping to potentially achieve even better clock performance and reduced quenching of the nuclear transition?

Beyond ThF4, several other host materials could be explored for 229Th doping to potentially enhance clock performance and reduce quenching of the nuclear transition. One promising candidate is Yttrium Aluminum Garnet (YAG), which has a high bandgap and excellent optical properties. YAG's crystalline structure could provide a stable environment for 229Th, potentially leading to reduced quenching effects.
Another potential host material is Lithium Fluoride (LiF), which has been used in various optical applications. LiF's low atomic number and high transparency in the ultraviolet range make it an attractive candidate for hosting 229Th, as it may minimize the interaction of the nuclear transition with surrounding electronic states.
Additionally, materials like Calcium Fluoride (CaF2) and Strontium Fluoride (SrF2) could be investigated. These materials have been previously used in optical applications and may provide suitable environments for 229Th doping, potentially leading to improved nuclear clock performance.
Lastly, exploring perovskite structures, such as Barium Titanate (BaTiO3), could also be beneficial. Perovskites often exhibit unique electronic properties and can be engineered to have high bandgaps, which may help in reducing quenching and enhancing the participation fraction of the nuclear transition.

Given the high emitter density in 229ThF4, what novel quantum optics phenomena beyond superradiance and coherent forward scattering might be observed in this system, and how could they be leveraged for practical applications?

The high emitter density in 229ThF4 thin films opens the door to several novel quantum optics phenomena beyond superradiance and coherent forward scattering. One such phenomenon is nuclear spin squeezing, which could be achieved through collective interactions among the densely packed 229Th nuclei. This effect could enhance the precision of measurements in quantum metrology applications, such as improving the stability and accuracy of nuclear clocks.
Another potential phenomenon is quantum interference effects arising from the coherent manipulation of nuclear states. By employing advanced laser techniques, it may be possible to create interference patterns that could be harnessed for high-resolution spectroscopy or imaging applications, allowing for the detection of weak signals or the study of complex quantum systems.
Additionally, the high emitter density could facilitate the observation of nuclear entanglement between 229Th nuclei. This entanglement could be leveraged for quantum information applications, such as developing quantum networks or enhancing the performance of quantum sensors.
Finally, the unique properties of the 229ThF4 system could enable the exploration of nuclear photonic devices, where the nuclear transitions are coupled to photonic structures. This could lead to the development of novel quantum light sources or quantum repeaters, which could significantly impact quantum communication technologies.
In summary, the exploration of these phenomena in 229ThF4 thin films could lead to practical applications in quantum metrology, quantum information processing, and advanced sensing technologies, paving the way for innovative developments in the field of quantum optics.