BBC – Quantum Computers ‘one step closer’

  • team used microwave energy to align two electron particles suspended in silicon, then used them to perform a set of test calculations
  • By using silicon, the scientists hope that quantum computers will be more easy to control and manufacture
  • research was published in the journal Nature
  • old adage of Schrödinger’s Cat is often used to frame a basic concept of quantum theory – use it to explain the peculiar, but important, concept of superposition; where something can exist in multiple states at once
    • Superposition is what makes quantum computing so potentially powerful.
  • To harness their (quantum/qubit) power, you have to link multiple qubits together, a process called entanglement
    • With each additional qubit added, the computation power of the processor is effectively doubled
  • generating and linking qubits, then instructing them to perform calculations in their entangled state – incredibly sensitive to external forces, which can give rise to errors in the calculations and in the worst-case scenario make the entangled qubits fall apart
    • One way to cope with this is to include additional qubits whose sole role is to vet and correct outputs for misleading or erroneous data
  • if quantum computers are going to take off, you need to come up with an easy way to manufacture large and stable qubit processors
  •  team of researchers, which also included scientists from the University of Wisconsin-Madison, turned to silicon to suspend single electron qubits whose spin was fixed by the use of microwave energy
    • In the superposition state, the electron was spinning both up and down
  • “The team managed to make a two qubit quantum gate with a very respectable error rate. While the error rate is still much higher than in trapped ion or superconducting qubit quantum computers, the achievement is still remarkable, as isolating the qubits from noise is extremely hard.”
    • remains to be seen whether error rates can be realised that are consistent with the concept of fault-tolerant quantum computing operation
  • in an accompanying paper, an international team, led by Prof Jason Petta from Princeton University, was able to transfer the state of the spin of an electron suspended in silicon onto a single photon of light
    • “If quantum gates in a solid state quantum computer can ever be realised with sufficiently low error rates, then this method could be used to connect different quantum computing modules which would allow for a fully modular quantum computer.”

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