Ytterbium atoms unlock quantum boost to 60-second magnetic coherence

Researchers affiliated with the Hefei National Research Center for Physical Sciences at the Microscale and the University of Science and Technology of China have achieved a spin coherence time of 60 seconds using ytterbium atoms, a duration that significantly exceeds typical cold-atom systems and promises more sensitive magnetic field sensors. The comagnetometer utilizes both isotopes of ytterbium, 171Yb (spin-1/2) and 173Yb (spin-5/2), jointly trapped within an optical lattice occupying approximately 160 lattice sites; vector and tensor light shifts are suppressed through polarization control and a Schrödinger cat state, respectively. This setup enables simultaneous Ramsey interferometry on both isotopes and achieves a magnetic noise suppression factor exceeding 3 x 10^4, while determining the ratio of nuclear magnetic moments to 4 parts per million precision. The results establish a new platform for spin-based sensing and may open pathways toward quantum-enhanced searches for physics beyond the Standard Model.

Ytterbium Isotopes Enable Long-Coherence Comagnetometry A spin coherence time of 60 seconds achieved using ytterbium atoms represents a considerable advancement in cold-atom comagnetometry and promises enhanced sensitivity for magnetic field sensors. Researchers affiliated with the Hefei National Research Center for Physical Sciences at the Microscale and the University of Science and Technology of China in Hefei demonstrated this extended coherence by jointly trapping the isotopes ytterbium-171 and ytterbium-173 within an optical lattice, a configuration that suppresses magnetic noise and enables precise measurements. This achievement surpasses typical cold-atom coherence times.

The team’s approach specifically addresses decoherence induced by light shifts, a common obstacle in utilizing cold atoms for precision measurements. The comagnetometer’s design relies on the distinct spin properties of the two ytterbium isotopes; 171Yb possesses a spin of 1/2, while 173Yb exhibits a spin of 5/2. This combination allows for simultaneous Ramsey interferometry, a technique used to measure the phase shift of atomic wavefunctions, and facilitates the suppression of magnetic noise. Vector light shifts, which arise from the polarization of the trapping laser light, are minimized by enforcing linear polarization of the optical lattice. The researchers employed a quantum control technique, preparing 173Yb atoms in a Schrödinger cat state, to eliminate tensor light shifts, interactions that can disrupt the coherence of higher-spin atoms. This careful manipulation of light interactions is crucial for maintaining the long coherence times observed in the experiment. The experimental setup begins with ytterbium atoms exiting an oven, undergoing Zeeman slowing, and being captured in a blue magneto-optical trap. Subsequent cooling stages, utilizing both green and blue MOTs, reduce the atomic temperature to approximately 20 microKelvin before transfer to a movable optical dipole trap and finally, the one-dimensional optical lattice. Approximately 2 x 10^4 atoms of each ytterbium isotope are confined within the lattice, occupying approximately 160 lattice sites, forming an ellipsoidal cloud measuring 40 micrometers in diameter and 80 micrometers in length. The atoms exhibit a lifetime of around 50 seconds within the optical lattice, demonstrating the stability of the trapping environment. A weak magnetic field (10-100 milligauss) is applied to define the spin quantization axis, providing a consistent reference frame for the measurements. To prepare the atoms for interferometry, a transversely polarized state is applied to 171Yb, while the 173Yb atoms are prepared in a Schrödinger cat state using a 556 nanometer Rabi beam. This beam induces specific Rabi transitions, carefully tuned to balance vector and tensor light shifts, ensuring the cat state’s insensitivity to these disruptive effects. The researchers note that the same Rabi beam also induces a small rotation on the spin of 171Yb, a factor accounted for in the data analysis. Simultaneous Ramsey interferometry is then performed on both isotopes, measuring the precession phase of their spin states. “We identify a novel systematic effect in the cat state stemming from the interplay between Zeeman and tensor light shifts,” the authors write, highlighting the complexity of controlling these quantum systems. This level of accuracy demonstrates the potential of this comagnetometer for high-precision measurements of fundamental physical constants and interactions. The ability to access much shorter distance scales, compared to traditional gas-cell systems, positions this technology for applications requiring localized sensing and high spatial resolution. The combination of long coherence times, high sensitivity, and the ability to control light-induced decoherence makes this system a promising tool for investigating a wide range of phenomena, from dark matter detection to precision tests of fundamental symmetries. The work by J.-L. Zhang, W.-T. Luo, Y. A. Yang, Y.-Q. Wang, T. Xia, and Z.-T. Lu, all affiliated with the Hefei National Research Center for Physical Sciences at the Microscale and the University of Science and Technology of China, represents a step forward in the field of quantum metrology and precision sensing.

Optical Lattice Confinement of Yb Atoms The optical lattice configuration also provides a degree of control not readily available in gas-cell systems. By manipulating the lattice parameters, beam power of 30 watts, waist of 25 micrometers, and wavelength, researchers can tailor the atomic density and spatial distribution, optimizing the sensor’s performance for specific applications. The lifetime of atoms in the optical lattice is observed to be 50 seconds, further contributing to the overall stability and sensitivity of the comagnetometer. The preparation of the Schrödinger cat state in 173Yb is particularly noteworthy. Unlike simpler polarization schemes, this requires a carefully tuned 556 nanometer Rabi beam, a laser pulse designed to induce specific transitions between atomic energy levels. The beam’s detuning from the relevant transitions is crucial, creating a balance between vector and tensor light shifts to achieve the desired immunity to decoherence. The same Rabi beam is also used to induce transitions in 171Yb, though it primarily affects the spin-1/2 system through vector shifts. The researchers emphasize the importance of minimizing crosstalk between the isotopes during this process, ensuring that the measurements accurately reflect the combined signal.

The team’s work demonstrates the power of combining advanced quantum control techniques with the unique properties of ytterbium atoms.

Second Spin Coherence Achieved in Yb Comagnetometer The team’s work, detailed in recent findings, moves beyond previous implementations limited to millisecond coherence by employing advanced quantum control techniques to suppress light-induced shifts in the atomic energy levels. The creation of this long-lived coherence relies on meticulous control of the optical environment surrounding the ytterbium atoms. Researchers constructed a one-dimensional optical lattice using a 30 watt laser focused to a 25 micrometer waist, a configuration enabling tight confinement of the atomic cloud. This lattice, crucial for maintaining atomic stability, occupies approximately 160 lattice sites and is specifically engineered to minimize unwanted interactions between the laser light and the atoms’ electronic structure.

The team further addressed tensor light shifts, a more complex phenomenon affecting the higher-spin 173Yb isotope, by preparing the atoms in a specially crafted quantum state known as a Schrödinger cat state. Preparing this Schrödinger cat state in 173Yb is particularly noteworthy, requiring a carefully tuned 556 nanometer Rabi beam. This precise manipulation of the laser parameters allows the 173Yb atoms to maintain their quantum coherence for an extended period. This is achieved through careful calibration and optimization of the laser pulses and magnetic field configurations. Unlike gas-cell systems, this cold-atom comagnetometer accesses much shorter distance scales, potentially enabling applications in areas where miniaturization and localized sensing are critical. Understanding and mitigating these systematic effects is crucial for achieving even higher precision in future experiments. Precision Measurement of Yb Nuclear Magnetic Moments The extended coherence allows for more precise measurements and opens possibilities for detecting subtle magnetic phenomena previously obscured by noise. Researchers carefully controlled the experimental environment, enforcing linear polarization of the lattice beam to eliminate vector light shifts, a common source of decoherence in optical lattices.

The team employed Ramsey interferometry, a technique that measures the phase accumulated during the free evolution of quantum states, simultaneously on both isotopes. This simultaneous measurement is crucial for exploiting the benefits of comagnetometry and achieving the observed coherence. Beyond extending coherence times, the team also focused on minimizing external noise. This suppression was accomplished through a combination of careful magnetic shielding and the inherent noise-canceling properties of the comagnetometer configuration. However, the path to such high precision was not without challenges. The researchers meticulously characterized this effect and developed strategies to minimize its impact on the final measurements, demonstrating a commitment to rigorous error analysis. This capability could prove invaluable in fields such as materials science, where probing magnetic properties at the microscale is essential, and in fundamental physics research, where searching for subtle interactions requires high spatial resolution. The ability to maintain coherence for 60 seconds opens up possibilities for more sensitive magnetic field sensors, potentially revolutionizing areas like biomagnetism and non-destructive testing.

The team’s work, detailed in their recent publication, demonstrates a significant step forward in the development of precision sensors and lays the groundwork for future investigations into fundamental physical phenomena. Source: https://www.nature.com/articles/s41566-026-01982-4 Stay currentSee today’s quantum computing news on Quantum Zeitgeist for the latest breakthroughs in qubits, hardware, algorithms, and industry deals. Tags: