Physics Colloquium: Photonic "Machine-Gun" for Deterministic Generation of Cluster States of Entangled Photons

Abstract:

We report on deterministic generation of long strings and cluster states of polarization entangled photons, highly resilient to qubit losses [1]. As such they are important resources for quantum information processing [1] and for quantum communication [2]. 

We practically realize a concept outlined in Ref [3]. The spin of an optically inactive electron-hole pair – a dark exciton– confined in a semiconductor quantum dot acts as entangler for generating the emitted photonic strings. The dark exciton is a long-lived matter spin qubit [4-5]. We initialize it in a coherent superposition of its two non-degenerate eigenstates [6], and its spin precesses with a time period of about 3 ns [4-5], which is much shorter than the qubit decoherence time (~ 100 ns [5]). Using repeated resonant excitation of the DE, every three quarters of its precession period, we coherently convert the dark exciton population into a coherent superposition of two electron hole pairs (biexciton) population. The biexciton decays radiatively rapidly, much faster than the spin precession time. The recombination entangles the remaining spin with the polarization of the emitted photon. By repeating this procedure at rates which can exceed 1 GHz, robust, deterministic entanglement between the polarization states of hundreds of photons can be achieved. 

Using polarization tomography we unambiguously demonstrate the deterministic generation of entangled photon strings and cluster states [7]. Our achievement may greatly reduce the resources needed for quantum information processing.

[1] R. Raussendorf and H. J. Briegel, Phys. Rev. Lett. 86, 5188 (2001)

[2] H. J. Briegel, W. D¨ur, J.I. Cirac, &P. Zoller, Phys. Rev. Lett. 81, 5932, (1998)

[3] N. H. Lindner and T. Rudolph, Phys. Rev. Lett, 103, 113602, (2009)

[4] E. Poem, Y. Kodriano, N.H. Lindner, D. Gershoni, et al, Nature Physics 6, 993, (2010)

[5] I. Schwartz, E. R. Schmidgall, D. Gershoni, et al, Phys. Rev. X. 5, 011009, (2015)

[6] I. Schwartz, D. Cogan, , E. R. Schmidgall, D. Gershoni, et al, Phys. Rev. B 92, 201201R (2015)

[7] I. Schwartz et al, "Deterministic Generation of a Cluster State of Entangled Photons", Science 10.1126/science.aah4758 (2016).

Event Organizer: Dr. Eran Sela