Noise & ErrorsΒΆ

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Noise is the uncontrolled interaction of the quantum system of interest with the Environment. It is one major source of errors, though it is not the only one.

Errors can be cast four different types (according to Lecture Notes 9 [M39]:

  • Incoherent errors:

    • Energy relaxation: A qubit in state \(\ket{1}\) will loose its excitation energy and spontaneously decay to its ground state \(\ket{0}\) (characteristic time \(T_1\)).

    • Dephasing: A qubit will also loose its phase information i.e. the relative phase between the \(\ket{0}\) and \(\ket{1}\) states will be altered (characteristic time \(T_2\)).

  • Leakage errors: Leakage out of the computational space e.g. excitation towards an additional state \(\ket{2}\). This can be triggered by the shape of the pulse.

  • Coherent errors: The control of the qubits is not perfect i.e. rotations by a given angle can only be done within a certain accuracy. The cumulation of small deviations will lead to qubit errors.

  • Measurement: The measurement process itself is prone to errors.

Using Quantum Computing will not be possible without significantly reducing the noise level and will require an efficiently implemented Error Correction.

More to explore:

  • Randomized Benchmarking [M8]:

    • apply random series of rotations in sphere, go back to \(\ket{0}\) (or \(\ket{1}\)) and check recovery .