The vacuum chamber of the new In+/Yb+-crystal clock houses an ion trap where ions are confined between gold electrodes. The clock utilizes a crystal composed of indium (pink) and ytterbium (blue) ions, representing a breakthrough in timekeeping technology. Developed by researchers at the Physikalisch-Technische Bundesanstalt (PTB) in Germany, this atomic clock operates on light frequencies instead of microwaves. This advancement could potentially enhance timekeeping precision by up to 1,000 times compared to current standards.
The current method for measuring time relies on the microwave frequency emitted by caesium atoms to define a second. However, optical clocks, like the one developed by PTB, tick at significantly higher frequencies, allowing for finer time resolution. By employing a chain of four ions in a compact 3D chip ion trap, the new clock achieves more accurate and reliable measurements. The ions are organized into a “Coulomb crystal” structure, isolated from external influences to maintain stability.
This innovative clock design combines indium and ytterbium ions to optimize timekeeping precision. Through careful ion positioning and monitoring using binary strings, the clock can maintain consistent performance. Additionally, a specialized imaging setup is employed to track the ion positions and ensure accurate control over the clock’s operation.
The system has the ability to restore a disrupted crystal by cooling it down, reshaping its form, or breaking apart molecules formed during gas collisions in the background. Keeping the clock synchronized: maintaining precision The laser of the clock must precisely match the energy level change of the indium ions. To achieve this, scientists utilize a stabilized Nd:YAG laser that operates at 946 nm. This laser is locked to a cryogenic silicon resonator to prevent any drift. The light is then converted to 230.6 nm to stimulate the indium ions. Illustrating the comparison of the clock: The innovative indium-ytterbium crystal clock was compared with the strontium lattice clock, ytterbium single-ion clock, and caesium fountain clock of PTB. (CREDIT: PTB) The clock’s cycle consists of four main stages: preparation, cooling, interrogation, and detection. Initially, the system inspects the crystal configuration to ensure proper ion alignment. The indium ion is then brought to a specific state. Subsequently, ytterbium ions cool the system through Doppler cooling. A 150-millisecond rectangular pulse examines the clock transition in the indium ion. Finally, a sensor verifies if the indium ion has made the anticipated leap. Any discrepancies in the crystal arrangement result in data being disregarded. Only outcomes from well-prepared crystals are retained to ensure precision. This approach not only enhances performance but also allows for scalability of the clock. The researchers have demonstrated its functionality with up to four ions, setting the stage for more complex arrangements. Precision-enhancing outcomes This clock has achieved a fractional systematic uncertainty of just 2.5 × 10⁻¹⁸—an extraordinary level of precision. For context, this is akin to measuring a second so accurately that it would only deviate by one second over 13.8 billion years. Coulomb crystal clock sequence: (a) chronological sequence, (b) decision flowchart. The crystal is initialized in the target permutation with interim reordering, cooling, and molecule separation steps. (CREDIT: Physical Review Letters) The PTB team juxtaposed their latest clock with two other optical clocks—one based on strontium atoms and the other on ytterbium ions. These comparisons yielded relative uncertainties of 4.2 × 10⁻¹⁷ and 4.4 × 10⁻¹⁸, respectively, showcasing an improvement of over ten times compared to prior measurements. These findings affirm the clock’s reliability and position it as a strong contender for future global time standards. The team also determined the absolute frequency of the indium transition, a crucial stride towards redefining the SI second. Currently, this redefinition hinges on establishing confidence in numerous optical clocks and validating their conformity through worldwide assessments. Jonas Keller, a physicist at PTB, highlighted the benefits of combining ion types: “We employ indium ions due to their favorable attributes for achieving
They have the ability to increase in size, speed, and outperform any other clock in the world. This paves the way for innovative concepts such as quantum many-body clocks or linked groups of atoms. It could potentially lead to advancements beyond timekeeping, including enhanced GPS, more accurate geophysical measurements, and experiments in fundamental physics. This research, which was published in Physical Review Letters, was supported by the German Research Foundation (DFG) as part of the Quantum Frontiers Cluster of Excellence and the DQ-mat Collaborative Research Center. These findings represent a significant development in precise timekeeping and bring us closer to a future where light is used to measure time.
