Atoms Entangled with Enhanced Control for Experiments

Researchers are continually seeking methods to enhance spin squeezing, a crucial resource for precision measurement. Zhiwei Hu from Fudan University, Youwei Zhang from Fudan University, and Junlei Duan from Fudan University, working with Mingfeng Wang from Wenzhou University and Yanhong Xiao from Fudan University, demonstrate a novel coherent control scheme to simultaneously boost collective spin squeezing and simplify the resulting atom-atom entanglement. This collaborative effort presents a protocol utilising a one-axis twisting echo sequence, effectively leveraging internal atomic states to optimise entanglement and encode it within two readily accessible magnetic sublevels. The significance of this work lies in offering a straightforward and efficient strategy for generating highly entangled states in multilevel atomic systems, circumventing the complexities of previous methods and paving the way for more practical applications in quantum technologies.

Scientists have devised a clever technique to improve the entanglement of atoms, bringing practical quantum technologies closer to reality. The method simplifies state control, overcoming limitations of previous approaches to generate more useful quantum states. This advancement promises more precise sensors and accelerates progress in harnessing the power of quantum mechanics.

Researchers have devised a new method for generating highly entangled states within atomic systems, potentially revolutionizing the precision of quantum sensors and accelerating the development of quantum technologies. This work addresses a longstanding challenge in quantum metrology, enhancing the sensitivity of measurements beyond the limitations imposed by standard quantum mechanics.

Existing techniques for boosting entanglement often rely on complex internal atomic states, hindering practical implementation and limiting the accessibility of these states for subsequent experiments. A coherent control scheme simultaneously amplifies collective spin squeezing and maps the resulting entanglement onto two readily definable magnetic sublevels within the atoms.

This innovative approach utilizes a carefully timed sequence of interactions, effectively “sandwiching” a quantum non-demolition measurement between two internal one-axis-twisting interactions arranged in an echo sequence. By optimally leveraging internal atomic states, the research overcomes limitations present in earlier methods, achieving a total squeezing coefficient slightly lower than the direct product of the internal and collective squeezing.

Once established, this entanglement is encoded in a simplified manner, directly within two magnetic sublevels, making it easily convertible into useful spin squeezing, a key resource for enhancing measurement precision. The study demonstrates a straightforward and efficient strategy for creating these highly entangled, yet accessible, quantum states in multilevel atomic systems.

Such advancements are poised to improve the performance of atomic clocks, interferometers, and magnetometers, extending their capabilities into new realms of sensitivity and accuracy. Achieving substantial improvements in quantum metrology demands increasingly sophisticated control over atomic systems. Conventional methods often struggle with the complexity of encoding collective squeezing in intricate superpositions of atomic states.

This new protocol offers a solution by employing a twisting echo sequence, a precisely orchestrated series of interactions, to amplify entanglement and simultaneously simplify its representation. At the heart of this technique lies the manipulation of internal atomic degrees of freedom, specifically leveraging one-axis-twisting interactions to enhance the coupling between atoms.

The true power of this approach resides in its ability to map the resulting entanglement onto two well-defined magnetic sublevels. This simplification is not merely a technical convenience; it is a critical step towards realising practical quantum sensors and devices. By avoiding complex state control, the research paves the way for more efficient manipulation and readout of spin states, essential for applications like Ramsey-type spectroscopy.

For decades, scientists have sought to harness the power of entangled atoms to surpass the standard quantum limit in measurement precision. Atoms in squeezed spin states (SSSs) offer a direct pathway to this enhancement, suppressing quantum fluctuations and enabling more sensitive detection. Most existing studies treat atoms as simple two-level systems, overlooking the potential of their multi-level structure.

This research directly addresses this limitation, demonstrating how to effectively utilise the internal states of atoms, each possessing a qudit system, to boost spin squeezing. At the core of the proposed method is a quantum non-demolition (QND) measurement, strategically positioned between two internal one-axis-twisting interactions. The initial OAT interaction amplifies quantum fluctuations, strengthening the QND interaction and increasing inter-atom entanglement.

Subsequently, the second, inverse OAT evolution maps this entanglement onto the two magnetic sublevels, creating a readily accessible form of spin squeezing. Analyses indicate that this echo-control protocol can enhance the optical depth of an atomic ensemble by up to a factor of 2f, offering a promising route to high-degree spin squeezing even in systems with limited optical depth.

Optimised interplay between internal states and collective squeezing enhances atomic entanglement

Researchers demonstrated a total squeezing coefficient slightly lower than the direct product of the internal and collective squeezing, representing a substantial advancement in generating entangled atomic states. This achievement bypasses limitations inherent in previous methods where internal squeezing diminished the efficiency of subsequent collective squeezing processes.

Specifically, the work details a method to optimise the interplay between internal atomic states and collective squeezing, yielding a measurable improvement in entanglement quality. A lower squeezing coefficient, in this instance, indicates a more efficient transfer of quantum properties and a stronger overall entangled state. The presented protocol sandwiches a non-demolition measurement between two internal one-axis-twisting interactions arranged in an echo sequence, allowing for optimal leveraging of internal states.

By encoding entanglement within two well-defined magnetic sublevels, the research offers a pathway to readily accessible states suitable for advanced quantum technologies. The significance extends beyond achieving a lower squeezing coefficient. At a fundamental level, the study showcases a method for boosting inter-atom entanglement while simultaneously preparing the system for practical applications.

For instance, the technique enhances the optical depth of an atomic ensemble by up to a factor of 2f, where ‘f represents the atomic spin level. Unlike prior approaches that relied on complex superpositions of magnetic sublevels, this work directly encodes the ensemble squeezing into two-level magnetic sublevels, simplifying state control and readout.

Once the internal one-axis-twisting interactions amplify single-spin quantum fluctuations, the subsequent quantum non-demolition measurement strengthens inter-atom entanglement. By reversing this process with a second internal one-axis-twisting interaction, the entanglement is mapped onto the two magnetic sublevels. The researchers successfully demonstrate full utilisation of the internal degrees of freedom for squeezing enhancement, paving the way for more precise quantum sensors and advanced quantum information processing.

Generating and mapping Heisenberg-limited spin squeezing via one-axis twisting

A coherent control scheme underpinned this work, simultaneously boosting collective spin squeezing and mapping atom-atom entanglement onto two defined magnetic sublevels. Initial preparation involved establishing a coherent spin state (CSS), where N identical spin-f atoms were initialised in the magnetic sublevel |f⟩, forming the basis for subsequent manipulations.

To maximise the uncertainty of the internal state, researchers employed a single-atom one-axis-twisting (OAT) interaction, described by HOAT = χ f 2 z, gradually stretching the uncertainty associated with fy. This interaction, applied for a specific time of π/2χ, generated a maximally entangled GHZ state, effectively linking electronic and nuclear spin, and achieving Heisenberg-limited uncertainty.

Simply creating squeezing within internal states isn’t enough; the team aimed to encode this squeezing in readily accessible magnetic sublevels. Following the initial OAT interaction, a collective quantum non-demolition (QND) measurement was performed, probing the anti-squeezed quadrature, the direction perpendicular to the initial squeezing, rather than along the squeezed direction itself.

This counter-intuitive approach strengthened the coupling of the QND interaction, enhancing inter-atom entanglement and ultimately boosting the overall spin squeezing. At this stage, the system existed as a superposition of multiple internal states, a configuration that complicates practical applications. Subsequently, a second, reversed internal OAT interaction was applied, functioning as an echo.

This inverse OAT evolution mapped the entanglement onto well-defined magnetic sublevels, demonstrating a twisting echo sequence designed to optimise squeezing and simplify state preparation. The entire protocol, illustrated in a schematic diagram, demonstrates a twisting echo sequence designed to optimise squeezing and simplify state preparation.

Simplified atomic control unlocks robust entanglement for quantum technologies

Scientists have devised a new method for generating entangled atomic states with greater efficiency and accessibility. For years, achieving strong entanglement, a bizarre quantum link between particles, has demanded complex control over atomic systems, often requiring intricate arrangements and limiting practical use. This research bypasses some of those hurdles, offering a pathway to create highly entangled states using a simpler, more direct approach.

Rather than relying on complicated superpositions, the team focused on a coherent control scheme that simultaneously enhances entanglement and confines it to easily manipulated atomic levels. The challenge wasn’t simply making entanglement, but making it useful. Previous techniques often encoded the entanglement in ways that were difficult to read out or integrate into other quantum systems.

Now, by carefully orchestrating interactions between atoms, researchers have successfully mapped the entanglement onto well-defined magnetic sublevels, making it readily available for subsequent experiments and applications. This improvement, reflected in a squeezing coefficient demonstrably better than previous designs, is not merely incremental; it suggests a potential shift in how we build and control quantum systems.

Translating laboratory success into real-world devices is rarely straightforward. Maintaining entanglement in a noisy environment remains a significant obstacle. Beyond this, scaling up the system, creating entanglement between many more atoms, will introduce new complexities. Once these hurdles are addressed, however, the implications are considerable.

More efficient entanglement generation could refine quantum sensors, allowing for more precise measurements of time, gravity, and magnetic fields. The field is poised for a period of rapid development. Unlike earlier methods that demanded exceptional precision, this technique offers a more forgiving pathway to strong entanglement. We can anticipate seeing this approach applied to a wider range of quantum technologies, from secure communication networks to advanced computing architectures. By simplifying the creation of entangled states, this research doesn’t just improve a technique; it broadens the possibilities for harnessing the power of quantum mechanics.