Single-Shot Measurement of One and Two-Electron Spin States in Si/SiGe Gated Quantum Dots

摘要

Single-shot measurement - the ability to make a projective measurement of a system without averaging over multiple repetitions of an experiment ?? is an important capability for quantum computation in general and quantum error correction in particular. Single-shot techniques also enable the extraction of more information about the dynamics of a system than can be extracted from average measurements alone. In this talk we discuss recent experiments involving single-shot measurements of electron spins in both a single-spin (up versus down) basis and a two-electron spin (singlet versus triplet) basis. In both cases, to measure the spin state we use a spin-to-charge conversion technique based on the energy difference between the two spin states. For single spins, this approach involves applying a magnetic field large enough that the Zeeman splitting between up and down spins E_z = g;C;_BB is larger than the electron temperature T. Here g ~ 2 is the g-factor, ;C;_B is the Bohr magneton, B is the magnetic field, and T ~ 140 mK for the single-spin experiments. For measurements of two-electron spin states, we make use of the energy difference between singlet and triplet states with two electrons in a single dot; in this case, we require the singlet-triplet splitting to be larger than the temperature T, which was less than 50 mK for the two-electron measurements.