A calibration sheet for a superconducting qubit lists and

PHYSICS · Multi-part · Fermi University Physics · Quantum Information & Technology · Open quantum systems, decoherence and error correction · Physical realizations and quantum technologies

Quantum Information and Technology, Ch Noise as a quantum operation

Problem

A calibration sheet for a superconducting qubit lists

T_1 = 80\,\mu\mathrm{s}

and

T_2 = 170\,\mu\mathrm{s}

. A technician defends the numbers: "Since

1/T_2 = 1/(2T_1) + 1/T_\phi

and

T_\phi

can be made as large as we like with better shielding, there is no upper limit on

T_2

relative to

T_1

; a measurement of

T_2 = 170\,\mu\mathrm{s}

alongside

T_1 = 80\,\mu\mathrm{s}

is therefore perfectly consistent." ((a)) Find the error in this argument. ((b)) State the largest value

T_2

can physically take for

T_1 = 80\,\mu\mathrm{s}

, and say whether the reported pair is consistent with it.

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