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Quantum Entanglement

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#51


How 'Alice and Bob' Test Quantum Mechanics

Imagine that A and B are entangled photons. A is sent to Alice and B is sent to Bob. Alice and Bob poke and prod at their photons in all kinds of ways to get a sense of their properties. Without talking to each other, they then each randomly decide how to measure their photons, using random number generators to guide their decisions. When Alice and Bob compare notes, they are surprised to find that the results of their independent experiments are correlated. In other words, even at a distance, measuring one photon of the entangled pair affects the properties of the other photon.

In reality, the photon detectors are not people, but superconducting nanowire single photon detectors (SNSPDs). SNSPDs are metal strips that are cooled until they become "superconducting," meaning they lose their electric resistance. A photon hitting this strip causes it to turn into a normal metal again momentarily, so the resistance of the strip jumps from zero to a finite value. This change in resistance allows the researchers to record the event.

To make this experiment happen in a laboratory, the big challenge is to avoid losing photons as they get sent to the Alice and Bob detectors through an optical fiber. JPL and NIST developed SNSPDs with worldrecord performance, demonstrating > 90% efficiency and low "jitter," or uncertainty on the time of arrival of a photon. This experiment would not have been possible without SNSPDs.

The design of this experiment could potentially be used in cryptography -- making information and communications secure - as it involves generating random numbers.

Cryptography isn't the only application of this research. Detectors similar to those used for the experiment, which were built by JPL and NIST, could eventually also be used for deep-space optical communication. With a high efficiency and low uncertainty about the time of signal arrival, these detectors are well-suited for transmitting information with pulses of light in the optical spectrum.
 
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#54
New state of quantum matter



An international team of researchers have found evidence of a mysterious new state of matter, first predicted 40 years ago, in a real material. This state, known as a quantum spin liquid, causes electrons - thought to be indivisible building blocks of nature - to break into pieces.

The observation of one of their most intriguing properties - electron splitting, or fractionalization - in real materials is a breakthrough. The resulting Majorana fermions may be used as building blocks of quantum computers.
 
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#60
By studying the light emitted from an extraordinarily dense and strongly magnetised neutron star using ESO's Very Large Telescope, astronomers may have found the first observational indications of a strange quantum effect, first predicted in the 1930s. The polarisation of the observed light suggests that the empty space around the neutron star is subject to a quantum effect known as vacuum birefringence.



Read full article here
 
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#69
A team of physicists at Aalto University in Finland has successfully created a Bose-Einstein condensate of light coupled with gold electrons, so-called surface plasmon polaritons.

 
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#72
Chinese scientists have successfully entangled 18 optical qubits by adopting a new technology called the multi-degree-of-freedom photon control method.


 
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#75
There was an episode of Star Trek in which some woman mentioned quantum mechanics. It puzzled the most brilliant of minds to this day.
 
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