Optimized Pulses Generate Highly Spin-Squeezed States in Rydberg Atom Arrays

Creating highly entangled quantum states is crucial for advancing technologies like quantum computing and sensing, and researchers are continually seeking more efficient methods to achieve this. Edison S. Carrera, Harold Erbin, and Gregoire Misguich, at Université Paris-Saclay, CEA, and CNRS, now demonstrate a powerful new technique for generating exceptionally well-ordered, or ‘spin-squeezed’, states in arrays of Rydberg atoms. Their method employs a precise, computer-designed sequence of pulses to manipulate the atoms, resulting in significantly greater entanglement than previously possible with standard approaches. The team’s optimised pulse sequences not only create states with record-breaking levels of squeezing, but also scale effectively to larger arrays, paving the way for more complex and powerful quantum systems.

The quest for increasingly precise measurements drives innovation across numerous scientific fields. A key limitation in many measurement scenarios is the inherent uncertainty dictated by the laws of quantum mechanics. However, by preparing quantum systems in carefully engineered states, it is possible to surpass these limitations and achieve sensitivities beyond what classical physics allows.

Researchers are now generating highly ‘squeezed’ quantum states in arrays of Rydberg atoms as a pathway to enhanced measurement precision. These states circumvent the limitations of quantum noise by reducing uncertainty in one direction, allowing for more precise measurements. This research introduces a new method for creating spin-squeezed states using quantum optimal control, leveraging the unique properties of Rydberg atom arrays – arrangements of atoms excited to a highly energetic state, allowing for strong, controllable interactions.

By precisely tailoring external electromagnetic fields, researchers can ‘steer’ the quantum state of the atom array towards a highly squeezed configuration. This is achieved through a gradient-based optimization technique, which systematically adjusts the control fields to maximize the degree of squeezing. The results demonstrate that this approach can generate highly spin-squeezed states in arrays containing up to eight atoms, approaching the theoretical limit for measurement precision.

Importantly, the optimized control sequences can be scaled to larger arrays – containing fifty atoms – achieving remarkably low squeezing parameters. This scalability is a crucial step towards building practical quantum sensors with significantly enhanced sensitivity. ## Optimal Control Generates Spin-Squeezed Rydberg Atom Arrays Researchers are employing a sophisticated approach to generate highly entangled states, known as spin-squeezed states, within arrays of Rydberg atoms.

This methodology centres on optimal control, a technique that precisely tailors external fields to steer the quantum system towards a desired configuration, contrasting with traditional methods that rely on passively evolving the system. The core innovation lies in using gradient-based optimization to design time-dependent pulse sequences. Researchers define a target spin-squeezed state and then employ an algorithm to iteratively refine the sequence of electromagnetic pulses applied to the atoms, effectively ‘sculpting’ the interactions between them.

The team measures the degree of spin squeezing using a parameter; values below one indicate a squeezed state with enhanced quantum correlations. A particularly noteworthy aspect of this work is the scalability of the method. The optimized pulse sequences aren’t limited to small arrays; they can be directly applied to significantly larger systems without requiring further optimization.

This is a major advantage, as building and controlling larger quantum systems is experimentally challenging. The researchers demonstrated this by achieving substantial spin squeezing in arrays containing fifty atoms, exceeding the performance of conventional methods. ## Highly Squeezed States with Rydberg Atom Arrays Researchers have achieved a significant advance in creating highly entangled states of matter using arrays of Rydberg atoms.

These atoms are ideally suited for quantum information processing, and this work demonstrates a powerful new method for squeezing quantum states to levels previously unattainable. The team developed a sophisticated control protocol that precisely manipulates the interactions between atoms, generating entanglement far exceeding that produced by simpler processes. By carefully designing time-dependent pulses of energy, researchers can steer the atoms into highly squeezed states – configurations where quantum uncertainty is reduced in one direction.

This squeezing is crucial for enhancing the precision of quantum measurements and improving the performance of quantum technologies. The method consistently approaches a fundamental limit on how much squeezing is possible, achieving results remarkably close to the theoretical minimum for systems containing up to eight atoms. Notably, this optimized control dramatically outperforms traditional approaches.

The team’s technique generates states with an entanglement depth exceeding six – meaning that at least six atoms are inextricably linked in a shared quantum state. The researchers discovered that many final states exhibit genuine multipartite entanglement – a complex form of correlation involving all the atoms in the array. Several states achieved high fidelity with a specific, highly entangled configuration known as a GHZ state, confirming the creation of robust, multi-atom entanglement.

Furthermore, the team demonstrated the ability to tailor the system, generating states with both high degrees of squeezing and strong collective magnetization – a property important for certain quantum applications. The control sequences developed are also surprisingly scalable, suggesting a pathway towards creating highly entangled states with a significantly increased number of atoms. ## Scalable Spin Squeezing with Optimal Control This research demonstrates a new method for creating highly spin-squeezed states in arrays of Rydberg atoms.

By employing optimal control techniques, the team successfully designed time-dependent pulse sequences that guide the atoms into highly entangled states with precisely controlled magnetization and squeezing direction. The method achieves spin-squeezing values approaching theoretical limits for small systems and, importantly, allows these optimized pulse sequences to be scaled to larger arrays while maintaining enhanced squeezing – a significant advantage over traditional methods. The results show that this approach not only generates highly squeezed states but does so in shorter timescales compared to conventional quantum quench protocols.

Furthermore, prioritizing high magnetization during the control process creates states more resilient to dephasing noise, a crucial consideration for practical experimental implementation. While the study focused on one-dimensional arrays, the authors suggest their quantum control framework can be adapted for two-dimensional geometries and extended to optimize other quantum properties, such as topological order. Future work will focus on adapting these control pulses to account for the specific constraints of existing Rydberg quantum simulators, paving the way for experimental validation on real devices.