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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Multiplexed quantum cryptography with single InP quantum dots

Thomas Aichele, Val Zwiller, Matthias Scholz, Gael Reinaudi, Jonas Persson, Oliver J. Benson

Published Apr 28, 2005• 4 citations
Publisher

Abstract

High-efficient single-photon sources are important for fundamental experiments as well as for modern applications in the field of quantum information processing. Therefore, both the overall collection efficiency as well as the photon generation rate are important parameters. In this article, we use cascaded two-photon emission from a single quantum dot in order to double the efficient transmission rate in a quantum key distribution protocol by multiplexing on a single photon level. The energetically non-degenerate photons are separated with a single photon add/drop filter based on a Michelson interferometer. For optimizing the collection efficiency, coupling of quantum emitters to microcavities is advantageous. We also describe preliminary results towards coupling of a single quantum dot grown on a micrometer-sized tip to the whispering gallery modes of a microsphere cavity.

DOI
10.1117/12.601824

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High-efficient single-photon sources are important for fundamental experiments as well as for modern applications in the field of quantum information processing. Therefore, both the overall collection efficiency as well as the photon generation rate are important parameters. In this article, we use cascaded two-photon emission from a single quantum dot in order to double the efficient transmission rate in a quantum key distribution protocol by multiplexing on a single photon level. The energetically non-degenerate photons are separated with a single photon add/drop filter based on a Michelson interferometer. For optimizing the collection efficiency, coupling of quantum emitters to microcavities is advantageous. We also describe preliminary results towards coupling of a single quantum dot grown on a micrometer-sized tip to the whispering gallery modes of a microsphere cavity.
Many important realizations and proposals for applications in quantum information processing require single photons as carriers of quantum information. Here, we review different demonstrations of quantum applications using a deterministic single-photon source based on InP/GaInP quantum dots. First, the single-photon generation is described and verified by autocorrelation measurements. A modification of the correlation setup allows the simultaneous observation of wave and particle properties of the photons. Additional to single-photon emission, photon pairs and triplets from multiexciton cascades were observed, as well. Using a Michelson interferometer an efficient separation of photon pairs can be achieved allowing multiplexing on a single-photon level. The applicability was demonstrated in a quantum key distribution experiment. As another application, different degrees of freedom of a single photon were used to realize a two-qubit Deutsch-Jozsa algorithm. Encoding the quantum information in appropriate bases, an operation of the setup resistant to phase fluctuation was demonstrated.
Many important realizations and proposals for applications in quantum information processing require single photons as carriers of quantum information. Here, we review different demonstrations of quantum applications using a deterministic single-photon source based on InP/GaInP quan- tum dots. First, the single-photon generation is described and verified by autocorrelation measurements. A modification of the correlation setup allows the simultaneous observation of wave and particle properties of the photons. Additional to single-photon emission, photon pairs and triplets from multi- exciton cascades were observed, as well. Using a Michelson interferometer an efficient separation of photon pairs can be achieved allowing multiplexing on a single-photon level. The applicability was demonstrated in a quantum key distribution experiment. As another application, different degrees of freedom of a single photon were used to realize a two-qubit Deutsch-Jozsa algorithm. Encoding the quantum information in appropriate bases, an operation of the setup resistant to phase fluctuation was demonstrated.
We present a two‐qubit quantum algorithm and multiplexed quantum cryptography as examples for quantum information processing using single photons generated in a single InP(GaInP) quantum dot. In the first part, a Deutsch‐Jozsa algorithm is executed with linear optics obtaining a fidelity of up to 79%, and noise‐resistant encoding is implemented by appropriate superpositions of spatial modes. In the second part, multiplexing enhances the bandwidth of quantum key distribution in a BB84 protocol.
We present the first demonstration of telecom fiber-based quantum key distribution using single photons from a quantum dot in a pillar microcavity. The source offers both telecommunication wavelength operation at 1.3 microns and Purcell enhancement of the spontaneous emission rate. Several emission lines from the InAs/GaAs quantum dot are identified, including the exciton-biexciton cascade and charged excitonic emission. We show an order of magnitude increase in the collected intensity of the emission from a charged excitonic state when temperature tuned onto resonance with the HE11 mode of the pillar microcavity, as compared to the off-resonance intensity. Above- and below-GaAs-bandgap optical excitation was used and the effect of the excitation energy on the photoluminescence investigated. Exciting below the GaAs-bandgap offers significant improvement in the quality of the single photon emission and a reduction of the multi-photon probability to 0.1 times the value for Poissonian light was measured, before subtraction of detector dark counts, the lowest value recorded to date for a quantum dot source at a fibre wavelength. We observe also the first evidence of Purcell enhancement of the spontaneous emission rate for a single telecommunication wavelength quantum dot in a pillar microcavity. We have incorporated the source into a phase encoded interferometric scheme implementing the BB84 quantum cryptography protocol and distributed a key, secure from the pulse splitting attack, over standard telecommunication optical fibre. We show a transmission distance advantage over that possible with (length-optimized) uniform intensity weak coherent pulses at 1310 nm in the same system.
Semiconductor quantum dots (QDs) coupled with optical microcavities provide an excellent platform for generating high-performance single-photon sources. However, the current microcavity structures are difficult to solve the tradeoff between single-photon purity and indistinguishability without additional filtering, due to challenges in suppressing broad phonon sideband spectrum and two-photon emission in the practical experiments. To address these issues, we have developed a novel asymmetric microcavity that supports two nondegenerate polarized modes, both resonant with a single quantum dot. One cavity mode is broadband and is used for excitation to reduce two-photon emission intensity, while the other is narrowband and is used for collection to enhance the indistinguishability of single-photon sources. This asymmetric microcavity also has the ability to overcome at least half of the photon efficiency loss under polarization filtering. Moreover, our model has employed an excitation pulse that resonates with cavity modes eliminating spectral distortion of intracavity fields, and efficiently achieving deterministic population inversion of QDs compared to an elliptical cavity. Our scheme paves the way to develop the excellent performance single-photon sources with higher brightness, near-unity purity, and indistinguishability without any additional filtering in practical experiments.