September Physicists in Germany have created a record-breaking optical version of a Schrödinger’s cat state, using highly excited atoms known as Rydberg atoms to generate an unusually large quantum superposition.

The experiment, led by researchers at the Max Planck Institute of Quantum Optics, produced optical cat states with a measured size parameter of α² = 2.4, surpassing the previous experimental value of 1.4 for comparable hybrid optical cat states.

What Is a Schrödinger’s Cat State?

Schrödinger’s cat is a famous thought experiment proposed by physicist Erwin Schrödinger in 1935 to illustrate the strange consequences of quantum mechanics.

In quantum physics, a system can exist in a superposition, meaning different possible states can coexist until measurement. The famous cat example was designed to show how unusual quantum rules become when extended from microscopic particles to the everyday world.

Scientists can create laboratory versions of these states using particles and light. The challenge is maintaining the fragile quantum connection while making the difference between the two states increasingly large.

Rydberg Atoms Help Create a Larger Quantum State

The German research team used extremely excited Rydberg atoms, whose unusual properties allow strong interactions between atoms and light.

The experiment combined an atomic ensemble with an optical resonator. The researchers used the atomic system to control the phase of light passing through the setup, allowing two different coherent light states to become linked to a control photon.

This produced a hybrid quantum state in which the two optical states remained connected through quantum superposition and entanglement.

New Record for Optical Cat States

The researchers created six different cat states and progressively increased their size.

The largest reached α² = 2.4, compared with the previous experimental record of 1.4 for this type of hybrid optical state. Measurements showed signatures of non-classical behaviour, including negative regions in the reconstructed Wigner function.

The researchers also found evidence that the largest state remained entangled. However, the experiment is still limited by losses and other sources of noise that become increasingly important as the quantum state grows.

Why the Experiment Matters

One of the major questions in quantum physics is why quantum behaviour is easily observed at microscopic scales but is much harder to maintain in larger systems.

Larger Schrödinger-cat states give researchers an opportunity to investigate the boundary between quantum and classical physics. They can also help scientists test theories that attempt to explain how quantum superpositions disappear through a process known as decoherence.

The experiment could eventually contribute to research into quantum information processing, quantum communication and precision measurements, although the current study does not demonstrate a commercial quantum-computing application.

Researchers See Room for Further Improvement

The experiment’s main limitations include photon loss, incomplete Rydberg blockade, laser phase noise and other imperfections that reduce quantum coherence.

The researchers indicate that improvements to the experimental setup could allow even larger cat states to be produced in the future. Whether those improvements can be demonstrated experimentally remains an open question.

The research is currently available as an arXiv preprint, meaning it has not yet undergone the standard peer-review process. Therefore, the reported record and its interpretation should be treated as preliminary until independent scientific review is completed.