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Does Schr枚dinger鈥檚 cat really exist? You bet. The first ever quantum superposition in an object visible to the naked eye has been observed.

, did not actually produce a cat that was dead and alive at the same time, as Erwin Schr枚dinger proposed in a notorious thought experiment 75 years ago. But they did show that a tiny resonating strip of metal 鈥� only 60聽micrometres long, but big enough to be seen without a microscope 鈥� can both oscillate and not oscillate at the same time. Alas, you couldn鈥檛 actually see the effect happening, because that very act of observation would take it out of superposition.

鈥淲e talk about quantum weirdness and things being in two places at once, but it all involves atoms and molecules, stuff we don鈥檛 normally interact with,鈥� says O鈥機onnell, who presented the results at the in Portland, Oregon, today.

Bridge between worlds

Proving that all objects, whatever their size, obeys the same rules has long been a goal of physicists. But with quantum mechanics it is no trivial matter: the larger an object, the more easily its fragile quantum state is destroyed by the disruptive influence of the world around it. O鈥機onnell鈥檚 experiments required delicate control and a temperature of just 25聽millikelvin to measure the state in the few nanoseconds before it was broken down by disruptive influences from outside.

鈥淚t was a close call, but sufficient to see a first quantum signature,鈥� says of the University of Vienna, Austria, who was not involved in the research.

The key was to connect the resonating strip to a superconducting qubit 鈥� a tiny electric circuit that can easily be prepared in a quantum superposition of two energy states. 鈥淭he qubit acts as a bridge between the microscopic and the macroscopic worlds,鈥� says O鈥機onnell. By tuning the frequency at which the qubit cycled between its two states to match the resonant frequency of the metallic strip, the qubit鈥檚 quantum state could be transferred to the resonator at will.

When measured afterwards, the resonator was sometimes in its non-oscillating ground state and sometimes in an oscillating 鈥渆xcited鈥� state. The number of times it was measured to be in each state followed the probabilistic rules of quantum mechanics.

Next, the cat?

鈥淚t鈥檚 like you have a child鈥檚 swing that goes back and forth,鈥� says O鈥機onnell. 鈥淲e pushed the swing and didn鈥檛 push the swing at the same time.鈥�

鈥淭his is challenging and creative work,鈥� says of Ludwig-Maximilian University Munich, Germany. 鈥淚f correct, it is a breakthrough.鈥�

Schr枚dinger鈥檚 cat would be unlikely to survive the frigid temperatures of such experiments, so it is perhaps not the next milestone to look out for. But now the spooky influence of quantum physics on visible objects has been proved, can we expect to be putting an object as large as a real child鈥檚 swing into an indeterminate quantum state any time soon? O鈥機onnell thinks so. 鈥淚鈥檇 say in the near future 鈥� in the next 20 years.鈥�

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