Quantum States Defy Time’s Arrow with Unprecedented Sensitivity for Measurement Devices

Researchers are developing innovative techniques to manipulate quantum states for enhanced precision measurements, and a new study details a method for generating Schrödinger-cat states using scalable entangling resources. Sebastián C. Carrasco, Michael H. Goerz, and Zeyang Li, alongside colleagues from institutions including the DEVCOM Army Research Laboratory, MIT-Harvard Center for Ultracold Atoms, and Ulm University, present a protocol employing rapid pulses to create these states with optimal Fisher information. This advancement is significant because it offers a pathway towards surpassing the classical limits of phase sensitivity and is compatible with a time-reversal strategy, potentially enabling practical applications in areas such as quantum metrology and sensing. The team also demonstrates resilience against realistic experimental losses, maintaining Heisenberg-limited scaling even with reduced twisting and atom numbers, thereby bolstering the feasibility of this approach.

Scalable Schrödinger-cat state generation via reduced shearing and time reversal

Scientists have developed a new technique for generating Schrödinger-cat states, quantum states defined as equal superpositions of coherent light fields, using a streamlined sequence of precisely timed pulses. This work demonstrates that the strength of the ‘shearing’ required to create these states, a measure of the manipulation needed, decreases proportionally to 1/√N, where N represents the number of atoms involved.

The resulting states exhibit optimal quantum Fisher information, a key metric indicating their suitability for surpassing the classical limits of phase sensitivity in applications such as quantum metrology. Notably, the protocol incorporates a time-reversal strategy, enhancing its practicality for real-world implementation.

This research introduces a method for creating Schrödinger-cat states with scalable entangling resources, offering a pathway to improved precision measurements. The team’s approach relies on a concise series of rapid ‘twist-and-turn’ pulses applied to the atomic system, effectively manipulating the quantum state.

A crucial finding is the inverse relationship between the required shearing strength and the number of atoms; increasing the atom count reduces the intensity of manipulation needed, simplifying the experimental requirements. This scaling behaviour is particularly significant as it facilitates the creation of more complex and robust quantum states.

The generated states are characterised by optimal quantum Fisher information, signifying their potential to outperform classical methods in phase estimation. This enhancement is vital for applications demanding high precision, including gravitational wave detection, atomic clocks, and fundamental tests of physics.

The protocol’s compatibility with a time-reversal strategy further solidifies its viability, allowing for the amplification of phase signals and achieving Heisenberg-limited scaling, a regime where measurement errors decrease proportionally to 1/N. This represents a substantial improvement over the standard quantum limit, where errors scale as 1/√N.

Furthermore, the study demonstrates that the Heisenberg limit scaling is maintained even when reducing the twisting applied alongside the number of atoms, effectively mitigating losses due to phenomena like photon scattering. This resilience to realistic experimental imperfections is a significant advancement, addressing a common challenge in quantum metrology.

By accounting for these losses, the researchers have shown that their method can reliably achieve ultra-high-precision sensing, paving the way for advancements in diverse research areas and potentially enabling new technologies reliant on precise measurements. The work details pulse sequences designed to generate these states and a time-reversal interferometric protocol to amplify signals.

Generating and characterising Schrödinger-cat states via time-reversal pulse sequences

A concise sequence of rapid twist-and-turn pulses forms the basis of a novel method for generating Schrödinger-cat states, defined as equal superpositions of arbitrary coherent states. The research demonstrates that the shearing strength required for this protocol scales linearly with time but decreases with increasing number of atoms (N) in proportion to 1/√N.

This reduction in required shearing strength is crucial for practical implementation and scalability of the technique. The resulting states exhibit optimal quantum Fisher information, indicating their suitability for surpassing the classical standard quantum limit of phase sensitivity in quantum metrology applications.

Notably, the protocol incorporates a time-reversal strategy for quantum metrology, ensuring practical viability through interferometric amplification of the acquired phase during free evolution. This time-reversal process involves subjecting the multi-atom quantum system to a pulse sequence, a period of free evolution, and then an inverse pulse sequence.

The work further demonstrates that the Heisenberg limit scaling remains intact even when reducing the twisting employed alongside the number of atoms. This mitigation of twisting directly addresses realistic losses, such as photon scattering, which can diminish coherence and reduce the effective atom number during measurement.

Implementation of this method is envisioned within an optical-lattice atom-clock experiment, leveraging engineered atom-atom interactions and standard rotation pulses. The study accounts for photon scattering, a common source of decoherence in such experiments, which projects sub-ensembles of atoms into excited states, thereby reducing the contributing atom number at the final measurement.

Analysis reveals that the proposed scheme successfully generates Schrödinger-cat states and achieves Heisenberg-limited scaling, paving the way for ultra-high-precision sensing across diverse research areas. The research establishes that these states are optimal for quantum metrology due to their enhanced sensitivity and resilience to decoherence.

Rapid pulse sequences yield high-fidelity Schrödinger-cat states with Heisenberg-limited scaling

Logical error rates of 2.9% per cycle were achieved through a novel method for generating Schrödinger-cat states using a concise sequence of rapid twist-and-turn pulses. The required shearing strength for this protocol decreases with increasing number of atoms, scaling proportionally to 1/√N, thereby enhancing efficiency.

These resulting states exhibit optimal Fisher information, positioning them as ideal candidates for surpassing the classical limit of phase sensitivity in diverse applications. The research demonstrates compatibility with a time-reversal strategy, ensuring practical viability for implementation. Specifically, the protocol maintains Heisenberg limit scaling even when reducing the twisting employed in tandem with the number of atoms, effectively mitigating realistic losses such as photon scattering.

For an atomic ensemble of N = 50, metrological gain was assessed targeting Schrödinger-cat states with varying angles, utilizing three OAT and Sx pulses with a fixed shearing strength. Metrological gain scaling exponents ranged between 0.9, observed for a phase angle of 0.2π, and 1.2, observed for 0.8π, surrounding the Heisenberg limit scaling.

It was determined that faster scaling than the Heisenberg limit is possible for a range of atomic numbers, though exceeding this limit remains unattainable. Reducing the normalized shearing strength to 0.4 resulted in a significant reduction in metrological gain at low atomic numbers, but approached the result obtained with a shearing strength of 1 as the number of atoms increased.

A shearing strength of 1 corresponded to a loss of 6.4 dB, while a value of 0.4 resulted in a loss of 2.5 dB, making the lower shearing strength preferable under these parameters. Prepared states were illustrated on the generalized Bloch sphere, revealing lower infidelity for low angles and higher shearing strengths.

Despite increasing ∆Sz during pulse sequence creation, the Fisher information remained high, sustaining the metrological gain even with moderate infidelities. This work demonstrates the generation of symmetric Schrödinger-cat states, useful for ultra-high-sensitivity sensing and metrology due to their Heisenberg limit scaling Fisher information. The protocol employs a time scaling proportional to 1/√N and does not require major modification to existing optical lattice clock atom experiment setups.

Rapid pulse sequences yield robust Schrödinger-cat states with Heisenberg-limited precision

Scientists have developed a new technique for generating Schrödinger-cat states, which are equal superpositions of coherent light states, utilising a sequence of rapid pulses. This method relies on alternating twist-and-turn pulses and demonstrates a decreasing requirement for shearing strength as the number of atoms increases, scaling inversely proportional to the square root of the atomic number.

The generated states exhibit optimal Fisher information, a key metric for precision in phase-sensitive applications, thereby surpassing classical limitations. This protocol is particularly noteworthy due to its compatibility with a time-reversal strategy, enhancing its feasibility for practical implementation in experiments such as optical lattice clocks.

Importantly, the technique maintains the Heisenberg limit scaling, a benchmark for precision, even when reducing the twisting action alongside decreasing atomic numbers, effectively mitigating the impact of realistic experimental losses like photon scattering. Analysis confirms that these symmetric Schrödinger-cat states maximise the quantum Fisher information, crucial for high-sensitivity sensing and metrology.

The authors acknowledge that the protocol’s performance is influenced by contrast loss arising from light-mediated interactions that also create the squeezing effect. Future research may focus on further optimising the pulse sequences and exploring the potential of this technique in diverse quantum applications, including quantum computing and precision measurement. The method’s compatibility with existing technology and favourable time scaling suggest a clear pathway towards improved quantum sensing capabilities without requiring substantial modifications to current experimental setups.