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Optically-probing spin qubit coherence without coherent control (Conference Presentation)
Author(s): Kai Müller; Alexander Bechtold; Fuxiang Li; Tobias Simmet; Nikolai A. Sinitsyn; Jonathan J. Finley
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Paper Abstract

We demonstrate an entirely new method to probe quantum measurement phenomena in semiconductor quantum dot (QD) spin qubits [1]. In addition to providing direct evidence for the quantum nature of solid state qubits, we show that our method has practical importance since it provides a completely alternative route for measuring ensemble and quantum dephasing times, T2* and T2, using only repeated projective measurements and without the need for coherent spin control. Our approach is based on measuring time-correlators of a spin qubit in an optically active QD beyond the second order. We utilize a quantum dot spin-storage structure to initialize a single electron spin in a quantum dot subject to a magnetic field applied in Voigt geometry through tunnel ionization and perform repeated projective measurements of the spin at times t1 and t2. This measurement is repeated, corresponding to ensemble averaging, and the resulting third-order time correlations reveals rich physics: For times t1 or t2 < T2* Larmor precession is observed which reveals the ensemble dephasing time T2*. Importantly, even though the time-correlators were obtained through averaging many measurements for times t1 and t2 > T2* oscillations are observed that decay with the dephasing time T2 and allow its determination even without the need for coherent spin control. Finally, combining the third-order time correlator with the second-order time correlator allows to demonstrate a violation of Leggett-Garg type inequalities for certain times providing clear evidence for the quantum nature of the quantum dot spin. [1] A. Bechtold et al. Phys. Rev. Lett. 117, 027402 (2016)

Paper Details

Date Published: 19 April 2017
PDF: 1 pages
Proc. SPIE 10102, Ultrafast Phenomena and Nanophotonics XXI, 101020F (19 April 2017); doi: 10.1117/12.2252812
Show Author Affiliations
Kai Müller, Walter Schottky Institut (Germany)
Alexander Bechtold, Walter Schottky Institut (Germany)
Fuxiang Li, Los Alamos National Lab. (United States)
Tobias Simmet, Walter Schottky Institut (Germany)
Nikolai A. Sinitsyn, Los Alamos National Lab. (United States)
Jonathan J. Finley, Walter Schottky Institut (Germany)


Published in SPIE Proceedings Vol. 10102:
Ultrafast Phenomena and Nanophotonics XXI
Markus Betz; Abdulhakem Y. Elezzabi, Editor(s)

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