& lead Physics 17, 92
Using an atomic array originally designed for quantum memory, researchers have demonstrated a magnetometer with unprecedented spatial resolution.
G. Birkl/Technical University of Darmstadt
Two-dimensional arrays of ultracold atoms are potential candidates for quantum memories and quantum computers, but they can also be used as sensors for detecting magnetic and other fields. Recently, a team at the Technical University of Darmstadt in Germany has demonstrated for the first time an atom array magnetometer whose spatial resolution exceeds that of classical devices. [1]. The result was presented last month by team leader Gerhard Birkl at the Atomtronics Conference in Spain.
Atomtronics is an emerging field in physics that aims to use atoms in analogy to electrons in traditional electronics. The term refers strictly to circuits in which atoms flow along laser-defined paths, but is often extended to other technologies that imply the manipulation of atoms with light. The experimental setup for this new study is indeed one based on laser cooling and laser blocking. “We are able to cool and arrange single rubidium atoms into two-dimensional arrays using light,” explains Birkl. The advantage of these widely adopted techniques – which were recognized with the Nobel Prize in Physics in 1997 – is that they do not require a complex cryogenic system, as other quantum technologies do.
In their lab, Birkl and colleagues trap rubidium atoms in a square-shaped array 0.2 mm wide. By means of an additional laser, which acts as optical tweezers, they can move each atom from one position to another. “We can create any model of atoms we want,” Birkl points out. So far, they have managed to place about 1,300 atoms in their array a few microns apart. However, the design can be scaled to 1 million atoms or more, according to Birkl.
This system can be used as a quantum memory, since each atom can be in one of two internal states, corresponding to the two possible states of a qubit. The system can also perform quantum calculations by exciting atoms into so-called Rydberg states that allow interactions between them. However, in the work presented in Spain, Birkl and his colleagues explored another direction: quantum sensing. The idea is to expose the system to a test magnetic field, which is static in time but varies in space. The system can probe these changes, as each atom of the array acts as a separate sensor. “It’s like having a CCD camera for magnetic fields,” comments Birkl. The pixel size of this camera is 7 µm, as this is the distance between the atoms in the cluster.
G. Birkl/Technical University of Darmstadt
To operate the system, the researchers started with all the atoms in their ground state. Then they turned on the magnetic field. The presence of this external field caused the two ground state energy levels of atoms to split into 12 different levels. The size of this energy split depends on the strength of the magnetic field and can be probed with high-resolution spectroscopy, a measurement process similar to how atomic clocks work.
In this way, the team can measure changes in the field with micrometer resolution and an accuracy of 100 nanotesla. They estimate that the smallest detectable field is 25 microteslas per second of measurement time, which roughly corresponds to the Earth’s magnetic field. This sensitivity is modest, but Birkl says the scheme is still in the early stages of development. By optimizing the parameters of the experiment, the researchers are confident that they can improve the sensitivity to 1 picotesla per second of measurement time. Such an optimized device can be used to determine the magnetic fields around some high-temperature superconductors that exhibit local asymmetry [2].
However, the potential applications are not limited to magnetometry. “Our sensor network platform can be extended to investigate electric fields, radio frequency waves and possibly gravitational fields,” adds Birkl. It can be useful for any application that requires high sensitivity and high spatial resolution, such as in materials science and biology. “This experiment is an important development in the field of quantum sensors,” says Donatella Cassettari, a cold atom expert from the University of St Andrews, UK, who was not involved in the study. “It relies on highly sophisticated techniques to manipulate the atomic state, yet has the potential to become a powerful and widely used sensor.”
-Andrea Parlangeli
Andrea Parlangeli is a science writer based in Milan, Italy. He is the author of A pure soul: Ennio De Giorgi, a mathematical genius (Springer, 2019)
References
- D. Schäffner et al.“Quantum Sensing in Tweezer Arrays: Optical Magnetometry in an Individual-Atom Sensor Network,” PRX Quantum 5010311 (2024).
- F. Yang et al.“Nematic transitions in iron pnictide superconductors imaged with a quantum gas,” Nat. Phys. 16514 (2020).
Subject areas
#Sensing #magnetic #fields #group #single #atoms
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