Single-shot read-out of an individual electron spin in a quantum dot

Abstract

Spin is a fundamental property of all elementary particles. Classically it can be viewed as a tiny magnetic moment, but a measurement of an electron spin along the direction of an external magnetic field can have only two outcomes: parallel or anti-parallel to the field [1]. This discreteness reflects the quantum mechanical nature of spin. Ensembles of many spins have found diverse applications ranging from magnetic resonance imaging [2] to magneto-electronic devices [3], while individual spins are considered as carriers for quantum information. Read-out of single spin states has been achieved using optical techniques [4], and is within reach of magnetic resonance force microscopy [5]. However, electrical read-out of single spins [6-13] has so far remained elusive. Here, we demonstrate electrical single-shot measurement of the state of an individual electron spin in a semiconductor quantum dot [14]. We use spinto-charge conversion of a single electron confined in the dot, and detect the single-electron charge using a quantum point contact; the spin measurement visibility is ∼ 65%. Furthermore, we observe very long single-spin energy relaxation times (up to ∼ 0.85 ms at a magnetic field of 8 Tesla), which are encouraging for the use of electron spins as carriers of quantum information.

Charge and Spin State Readout of a Double Quantum Dot Coupled to a Resonator

“…3(a) which were acquired with an effective bandwidth of B = 3 Hz, (3 kHz low-pass filter and 10 3 averages) we estimate a minimum detection time of τ m ∼ 4 ms for a signal-to-noise ratio of one. This measured minimum detection time is comparable with typical spin lifetimes in GaAs [4]. We expect that this time could be improved by a factor of ∼ 30 with optimal driving and by reducing resonator losses.…”

“…Non-invasive detection using a QPC has been critical to recent advances in coherent control of few-electron double quantum dots [2], allowing their charge configurations to be mapped in regimes where transport through the double dot itself is not measurable [3]. Furthermore, through spin-to-charge conversion techniques, spin state measurements of single and double dots have been demonstrated using QPCs [4,5].Resonant microwave circuits have played an important role in performing sensitive measurements of mesoscopic devices. In the case of superconducting charge qubits, earlier schemes used a proximal single electron transistor (SET) charge detector to perform state readout [6,7].…”

The ultra-sensitive electrical detection of spin-Rabi oscillation at paramagnetic defects

“…In order to achieve higher sensitivities, magnetic resonance methods have been combined in the past with other measurement techniques such as force microscopy [1], photoluminescence [2,3] or conductivity measurements [4,5] which have all reached single spin detection sensitivity in recent years. Among these methods, the electrically detected magnetic resonance (EDMR) technique may be most beneficial for the spin spectroscopy of semiconductors since naturally, it is very sensitive to centers which influence conductivity while it is blind to all other spins.…”

Double detected spin-dependent quantum dot

“…While the system described above is similar to the spin-to-charge conversion in quantum dots [8,9], the model of the unsharp detector is different. Here, the back-action of continuous quantum measurement on magnetization is investigated by a detected electric current, focusing on measurement back-action and on QZE in the spin states.…”