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Wigner sharpened the paradox by imagining a (human) friend of his shut in a lab, measuring a quantum system. He argued it was absurd to say his friend exists in a superposition of having seen and not seen a decay unless and until Wigner opens the lab door. [Nora] Tischler and her colleagues have carried out a version of the Wigner’s friend test. By combining the classic thought experiment with another quantum head-scratcher called entanglement—a phenomenon that links particles across vast distances—they have also derived a new theorem, which they claim puts the strongest constraints yet on the fundamental nature...

Quantum mechanics’ core assumption is that on the smallest scales, atomic properties are quantized...For example, an electron can be in a lowest-energy state, but if you add a little more energy, it doesn’t slowly transition into the new higher-energy state. Rather, it unpredictably snaps into the new state. If you’re not looking at it, the atom can take on intermediate states—but these aren’t midway points. The atom would be in both states at the same time, and then once you observed it, it would immediately snap into one state or the other. The team’s artificial atom is an experimental apparatus...

An old thought experiment now appears in a new light. In 1935 Erwin Schrödinger formulated a thought experiment designed to capture the paradoxical nature of quantum physics. A group of researchers led by Gerhard Rempe, Director of the Department of Quantum Dynamics at the Max Planck Institute of Quantum Optics, has now realized an optical version of Schrödinger's thought experiment in the laboratory. In this instance, pulses of laser light play the role of the cat. The insights gained from the project open up new prospects for enhanced control of optical states, that can in the future be used for...

Physicists have learned how they could breed Schrödinger cats in optics. Scientists tested a method that could potentially amplify superpositions of classical states of light beyond microscopic limits and help determine the boundaries between the quantum and classical worlds. ... Co-author and University of Calgary graduate student Anastasia Pushkina explains: "The idea of the experiment was proposed in 2003 by the group of Professor Timothy Ralph of the University of Queensland, Australia. In essence, we cause interference of two "cats" on a beam splitter. This leads to an entangled state in the two output channels of that beam splitter. In...

Science Daily — Australian and French scientists have made another breakthrough in the technology that will drive next generation computers and teleportation. The researchers have successfully superposed light beams, which produces a state that appears to be both on and off at once. Light beams that are simultaneously on and off are vital for the next-generation super computers which should be faster than current computers based on bits, that are either on or off. Previously, only smaller light particles had been superposed and the group has also proved a quantum physics theory known as Schrödinger's cat. This theory, named after...