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Spin Lifetimes in Quantum Dots from Noise Measurements
J. Wabnig, B.W. Lovett, G.A.D. Briggs, J.H. Jefferson
If we look at an electrical current, the flow of charges is not regular, but actually fluctuating due to temperature and external influences. In electrical engineering this is usually unwanted and is designated as noise. But there is actually information to be found in the fluctuations of the current.
In our recent letter “Spin Lifetimes in Quantum Dots from Noise Measurements”, accepted for publication in Physical Review Letters, we investigate theoretically how fluctuations can help us to learn more about spin lifetimes in a quantum dot. We imagine a scenario where an electrical current is passed through a quantum dot in a magnetic field under microwave irradiation. The current through the dot depends on the populations in the different spin states. If the microwave frequency is close to the on-dot Zeeman splitting the populations start to change as a function of the applied magnetic field as the dot spin is driven towards saturation. The width of this transition gives us information about the ratio of the spin relaxation time T1 and the spin coherence time T2 (see Fig. (a)). Considering the fluctuations of the current, i.e. the current-current correlations, at resonance, we obtain a distinct dip in the noise power spectrum at the Rabi frequency. The width of this dip is given by the average of T1 and T2 (see Fig. (b)) and we can thus obtain full information about spin lifetimes from electrical transport measurements.
Our method would not require pulsed gates, the measurement can be achieved in a stationary state and it works well for temperatures comparable to the Zeeman splitting.
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