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The IBM Quantum team envisions a future where quantum computers interact frictionlessly with high performance computing resources, taking over for the specific problems where quantum can offer a computational advantage. Pushing the envelope of classical computing is crucial to this goal, especially as we develop new quantum algorithms and try to understand which problems are worth tackling with a quantum computer.

A large team of researchers working with Google Inc. and affiliated with a host of institutions in the U.S., one in Germany and one in the Netherlands has implemented a quantum approximate optimization algorithm (QAOA) on a 53-qubit noisy intermediate-scale quantum (NISQ) device. In their paper published in the journal Nature Physics,, the group describes their method of studying the performance of their QAOA on Google's Sycamore superconducting 53-qubit quantum processor and what they learned from it. Boaz Barak with Harvard University has published a News & Views piece on the work done by the team in the same journal issue.

Noise limits the performance of modern quantum technologies. However, particles traveling in a superposition of paths can bypass noise in communication. A collaboration between the Universities of Hong-Kong, Grenoble and Vienna, as well as the Austrian Academy of Sciences, under the lead of Philip Walther, reveals novel techniques to reduce noise in quantum communication. The results, published in the latest issue of Physical Review Research, demonstrate that quantum particles traveling in a superposition of paths enable noise reduction in communications.

"Spooky action at a distance," Einstein's summation of quantum physics, has been a criticism of quantum mechanics since the field emerged. So far, descriptions of entangled particles to explain their apparently faster-than-light responses, and even explanations for the phase shifts induced by an electromagnetic field in regions where it is zero-the "Aharonov-Bohm" effect-have mostly addressed these concerns. However, recent theoretical and experimental demonstrations of a "counterfactual" quantum communication protocol have proved difficult to explain in terms of physical cause and effect. In this kind of quantum communication, observers on either side of a "transmission channel" exchange information without any particle passing between them-spooky indeed.

Physicists who think carefully about time point to troubles posed by quantum mechanics, the laws describing the probabilistic behavior of particles. At the quantum scale, irreversible changes occur that distinguish the past from the future: A particle maintains simultaneous quantum states until you measure it, at which point the particle adopts one of the states. Mysteriously, individual measurement outcomes are random and unpredictable, even as particle behavior collectively follows statistical patterns. This apparent inconsistency between the nature of time in quantum mechanics and the way it functions in relativity has created uncertainty and confusion.

Researchers in China claim to have achieved quantum supremacy, the point where a quantum computer completes a task that would be virtually impossible for a classical computer to perform. The device, named Jiuzhang, reportedly conducted a calculation in 200 seconds that would take a regular supercomputer a staggering 2.5 billion years to complete.

Normally, causal influence is assumed to go only one way-from cause to effect-and never back from the effect to the cause-the ringing of a bell does not cause the pressing of the button that triggered it. Now, researchers from the University of Oxford and the Université libre de Bruxelles have developed a theory of causality in quantum theory, according to which cause-effect relations can sometimes form cycles. This theory offers a novel understanding of exotic processes in which events do not have a definite causal order. The study has been published in Nature Communications.

Anyons have characteristics not seen in other subatomic particles, including exhibiting fractional charge and fractional statistics that maintain a "memory" of their interactions with other quasiparticles by inducing quantum mechanical phase changes.

The result highlights a fundamental tension: Either the rules of quantum mechanics don't always apply, or at least one basic assumption about reality must be wrong.