Quantum mechanics

  • Quantum mechanics (QM) is the dark arts of physics.
  • Though physics — in the Newtonian mould — tells us how every object will precisely behave when pushed and hurled, QM deals with the invisible world of subatomic particles, where counter-intuitive rules apply.
  • QM inhabitants such as electrons and photons live in zombie-like ‘undead’ states.
  • The very act of observing them makes them beguiling tricksters.
  • Though not always understandable, science knows, in bits and pieces, how they can be manipulated for purposes that benefit the visible world such as making integrated circuit chips and fibre-optic lines for global, instantaneous communication.
  • One of quantum mechanics’ cardinal principles, of Heisenberg Uncertainty, follows that no physical object can be known entirely.
  • Measuring, say, its momentum with increasing precision reduces the accuracy with which you can determine its position.
  • For long this was seen as a barrier imposed by nature to us fully comprehending a physical system but for a few decades now, the field of quantum cryptography has evolved around designing ‘keys’ or alpha-numeric codes exploiting quantum mechanical strictures.
  • The Chinese set-up transferred entangled photons through a satellite, called Micius, between two ground stations that were 1,200 km apart.
  • According to a report in Science News, the researchers shot a laser beam into a light-altering crystal in the satellite.
  • The crystal emitted pairs of photons entangled so that their polarisation states (or how they are oriented in space) would be opposite when one was measured.
  • The pairs were split, with photons sent to separate receiving stations in Delingha and Lijiang, which are telescopes on mountains, 1,200 km apart.
  • Both stations are in the high mountains of Tibet, reducing the amount of air the fragile photons had to traverse.
  • This team then simultaneously measured more than 1,000 photon pairs.
  • They found the photons had opposite polarisations far more often than would be expected by chance.
  • The technological challenge in this case was ensuring that the transmission between the satellites and ground observatories was so steady that the stream of hyper-sensitive, journeying photons weren’t broken even though the satellite was cruising at nearly 8 km per second. “…
  • The obtained link efficiency is [in] orders of magnitude higher than that of the direct bidirectional transmission of two photons through telecommunication fibres,” says an accompanying press statement.


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