The nitrogen-vacancy (NV) centre has a spin-1 ground state split by zero-field…
PHYSICS · Multi-part · Fermi University Physics · Quantum Mechanics · Quantum Information & Technology · Physical realizations and quantum technologies
Quantum Information and Technology, Ch Trapped ions, neutral atoms, photons, NMR and spins in solids
Problem
The nitrogen-vacancy (NV) centre has a spin-1 ground state 3A2 split by zero-field splitting D=2.87GHz into ms=0 and the (near-degenerate at low field) ms=±1 sublevels, an excited triplet reached by a 532nm green laser, and a metastable singlet that the excited state decays into preferentially from ms=±1 rather than from ms=0; decay from the singlet returns the system to ms=0 in the ground state. A silicon spin qubit is a single electron confined in a gate-defined quantum dot, addressed by microwave electron spin resonance (ESR) and by exchange pulses between neighbouring dots, and read out by spin-selective tunnelling to a reservoir, converted to a charge signal on a nearby charge sensor.
((a)) For the NV centre, identify which physical process in the description above realises (i) initialisation into a known spin state, (ii) coherent control of the spin state, and (iii) readout of the spin state. State the state that is prepared and the observable signature (bright or dark) of each spin sublevel on readout.
((b)) For the silicon spin qubit, identify the physical process that plays the same role as each of the three NV steps: initialisation, control and readout. Name the physical quantity actually measured at readout and explain how spin information becomes that quantity.
((c)) State one respect in which the readout mechanisms of the two platforms differ in what they directly detect (a photon count against a charge/current signal), and explain why this difference does not change the fact that both are projective measurements of the spin.