Event

Quantum information based on optical cavities often utilizes atomic Λ-systems consisting of two Zeeman split levels connected by common excited states. However, the exploration of solid-state Λ-systems coupled to cavities is only now beginning. Long-lived spin states in charged InAs quantum dots (QDs) are known to form a Λ-system and have been demonstrated as an optically addressable spin qubit [1]. Our collaboration has previously incorporated a singly charged InAs quantum dot (QD) within a doped GaAs photonic crystal cavity, successfully demonstrating qubit operations [2] as well as cavity-stimulated Raman emission [3]. Subsequent work has also realized a spin-photon quantum switch in a QD-cavity system [4]. However, a drawback of single QDs is that the Zeeman splitting is often smaller than the cavity linewidth, making it challenging to selectively enhance different branches of the QD Λ-system and achieve spin-cavity interactions.

In this seminar I will present our efforts to overcome this limitation by developing a cavity-coupled quantum dot molecule (QDM) [5]. The properties of QDMs (two QDs separated by a coherent tunnel barrier) can be finely tuned during growth and each QD can be charged with an electron leading to a singlet-triplet Λ-system. The singlet-triplet splitting can be controlled by engineering the tunnel barrier, allowing us to design a structure where the splitting is almost an order of magnitude larger than the cavity linewidth. This is a new spectroscopic regime where the cavity can be coupled to either the excitation branch or the emission branch of the Λ-system. Tuning the cavity to the excitation branch, we drive the QDM system into the nonlinear regime to investigate the Autler-Townes state dressing and laser-induced control of the spin exchange energy. These results may lead to new avenues in quantum information processing and advance prospects for an all-optical quantum network. Time permitting, I will also discuss our recent demonstration of a V-system strongly coupled to an optical cavity mode, a configuration that enables voltage-controlled cavity-QDM interactions.

[1] A. J. Ramsay, Semicond. Sci. Technol. 25, 103001 (2010).

[2] S. G. Carter, T. M. Sweeney, M. Kim, C. S. Kim, D. Solenov, S. E. Economou, T. L. Reinecke, L. Yang, A. S. Bracker, and D. Gammon, Nat. Photonics 7, 329 (2013).

[3] T. M. Sweeney, S. G. Carter, A. S. Bracker, M. Kim, C. S. Kim, L. Yang, P. M. Vora, P. G. Brereton, E. R. Cleveland, and D. Gammon, Nat. Photonics 8, 442 (2014).

[4] S. Sun, H. Kim, G. S. Solomon, and E. Waks, Nat. Nanotechnol. AOP, (2016).

[5] P. M. Vora, A. S. Bracker, S. G. Carter, T. M. Sweeney, M. Kim, C. S. Kim, L. Yang, P. G. Brereton, S. E. Economou, and D. Gammon, Nat. Commun. 6, 7665 (2015).