Controlled Phase Shifts with a Single Quantum Dot

doi:10.1126/science.1154643

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Physics

Science 9 May 2008:
Vol. 320. no. 5877, pp. 769 - 772
DOI: 10.1126/science.1154643

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Reports

Controlled Phase Shifts with a Single Quantum Dot

Ilya Fushman,¹^* Dirk Englund,¹^* Andrei Faraon,¹^* Nick Stoltz,² Pierre Petroff,² Jelena Vu $c$ kovi $c$ ³

Optical nonlinearities enable photon-photon interaction andlie at the heart of several proposals for quantum informationprocessing, quantum nondemolition measurements of photons, andoptical signal processing. To date, the largest nonlinearitieshave been realized with single atoms and atomic ensembles. Weshow that a single quantum dot coupled to a photonic crystalnanocavity can facilitate controlled phase and amplitude modulationbetween two modes of light at the single-photon level. At largercontrol powers, we observed phase shifts up to ${pi}$ /4 and amplitudemodulation up to 50%. This was accomplished by varying the photonnumber in the control beam at a wavelength that was the sameas that of the signal, or at a wavelength that was detuned byseveral quantum dot linewidths from the signal. Our resultspresent a step toward quantum logic devices and quantum nondemolitionmeasurements on a chip.

¹ Applied Physics, Stanford University, Stanford, CA 94305, USA.
² Electrical and Computer Engineering, University of California, Santa Barbara, CA 93106, USA.
³ Electrical Engineering, Stanford University, Stanford, CA 94305, USA.

^* These authors contributed equally to this work.

To whom correspondence should be addressed. E-mail: jela{at}stanford.edu