In a significant advance for quantum measurement, a team of physicists in Amsterdam has determined a fundamental property of the strontium atom with unprecedented accuracy by using a neighboring cloud of rubidium atoms as a precise calibration tool. The innovative technique, which involves trapping and measuring two different atomic species simultaneously, overcomes long-standing barriers in precision and provides a measurement 100 times more accurate than previous efforts.
The work holds profound implications for the future of technology, particularly in the development of next-generation atomic clocks and quantum computers. Strontium is a leading element for these applications due to its unique atomic structure, but harnessing its full potential requires an exceptionally precise understanding of its properties. By using well-understood rubidium atoms to correct for experimental uncertainties, the researchers have created a new benchmark for atomic measurements that could accelerate the development of more powerful and stable quantum devices.
A Two-Species Solution
The experiment centered on isolating and controlling two different elements in an ultracold trap. The primary atom of interest was strontium-87, a specific isotope of strontium whose nucleus behaves like a tiny, powerful magnet. Understanding the exact strength of this nuclear magnet is critical for its use in advanced technologies. The key challenge in measuring this property, known as the nuclear g-factor, is that it is sensitive not only to the nucleus itself but also to the cloud of electrons surrounding it and to the precise strength of any external magnetic field applied during the experiment.
To solve the problem of environmental interference, the physicists introduced a second atomic element into the trap: rubidium. The properties of rubidium are already known with extremely high precision. By placing the rubidium atoms in close proximity to the strontium, the team created an integrated system where both atomic species experienced the exact same magnetic field. The rubidium cloud effectively became a highly sensitive probe, or quantum sensor, allowing the researchers to measure the local magnetic field with an accuracy that was previously unattainable.
Overcoming Magnetic Field Instability
Measuring the properties of a single atom’s nucleus requires placing it in a strong, stable magnetic field. This technique takes advantage of a quantum mechanical phenomenon first observed in the 19th century.
The Zeeman Effect
The principle behind the measurement is the Zeeman effect, where a magnetic field causes the distinct energy levels within an atom to split into multiple sub-levels. For the strontium-87 isotope, its nucleus gives it a property called “nuclear spin,” which results in ten distinct energy states when a field is applied. The spacing of these energy levels is directly proportional to the strength of the nuclear magnet, or its g-factor. By measuring the frequency of light needed to make the atom jump between these split levels, scientists can calculate the g-factor. However, even the slightest fluctuation or imperfection in the magnetic field can introduce errors, limiting the precision of the measurement.
A Precise Atomic Reference
This is where the rubidium atoms played their crucial role. Because the rubidium atoms were interspersed with the strontium, they provided a real-time, in-place reference for the magnetic field’s strength. By simultaneously measuring the energy level splitting in the well-understood rubidium atoms, the team could precisely calculate the magnetic field being experienced by the strontium atoms. This allowed them to eliminate the magnetic field as a source of uncertainty, isolating the measurement to the strontium’s intrinsic nuclear properties. The result was a dramatic improvement in the accuracy of the g-factor, setting a new record.
Implications for Clocks and Computers
The successful measurement, published in the journal Physical Review Letters, is more than a feat of technical skill; it paves the way for significant technological advancements by refining our understanding of a uniquely useful atom.
More Accurate Atomic Clocks
Strontium-87 is a cornerstone for the world’s most accurate timekeeping devices: optical atomic clocks. These clocks use the frequency of light absorbed by strontium atoms as a “pendulum” that is billions of times more stable than traditional clocks. Such devices are essential for GPS navigation, data synchronization across the internet, and deep-space exploration. By providing a more precise value for the strontium g-factor, this research allows for even better control and understanding of the atom, which will help engineers reduce systemic errors and build more stable and accurate clocks.
Robust Quantum Computing
The complex internal structure of strontium-87 also makes it an attractive candidate for quantum computing. The ten distinct energy levels provided by its nuclear spin can be used to encode information, serving as quantum bits (qubits) or even more complex “qudits.” A qudit, which can exist in more than two states, offers a way to store and process much more information than a standard qubit. The development of a reliable quantum computer depends on the ability to precisely control and manipulate these quantum states. The improved g-factor measurement provides the fundamental data needed to exert that control with higher fidelity, reducing errors and advancing the frontier of quantum information science.
A New Horizon for Physics Research
The dual-species measurement technique pioneered by the Amsterdam team provides a powerful new tool for the physics community. It could be adapted to measure the properties of many other atoms that are important for fundamental science but have been difficult to characterize with high precision. This could open doors to new investigations into the fundamental laws of nature, including more sensitive searches for dark matter or tests of whether the fundamental constants of the universe are truly constant over time.
While the team’s initial goal was to create molecules from rubidium and strontium, their innovative workaround has established a new standard in the field of atomic physics. The ability to use one quantum system to precisely probe another highlights a growing trend in physics, where the mastery of control over the atomic world leads to discoveries that echo across multiple scientific and technological disciplines. The humble strontium atom, when observed by its well-behaved neighbor, has revealed its secrets with newfound clarity.
