Matthias Scholz

Non-classical light emission from a single electrically driven quantum dot

Easy to handle light sources with non-classical emission features are strongly demanded in the growing field of quantum communication. We report on single-photon emission from an electrically pumped quantum dot with unmatched spectral purity, making spatial or spectral filtering dispensable.

Narrow-band single photons from a single-resonant optical parametric oscillator far below threshold

We present a single-resonant optical parametric oscillator pumped far below threshold as a source for narrow-band single photons. Spontaneous generation of single photons via parametric downconversion is modified and follows the cavity transfer function. Cross-correlation measurements between signal and idler beams show a cavity bandwidth of 62MHz. As the main improvement to prior realizations, our cavity is locked to the pump beam via the Hansch-Couillaud method and therefore allows the continuous generation of heralded single photons with long-term stability.

Single-mode operation of a high-brightness narrow-band single-photon source

We demonstrate a narrow-band single-photon source based on cavity-enhanced parametric downconversion for efficient coupling to atomic quantum memories. Selecting a single longitudinal cavity mode by spectral filtering, we achieve a spectral brightness of ∼330 biphotons/(s mW MHz) and an overall bandwidth of 2.7 MHz, which suits the width of naturally broadened transitions in alkali gases like rubidium or cesium.

Offset compensation by use of amplitude-modulated sidebands in optical frequency standards

We present a general method for continuously measuring and compensating for offsets (due to residual amplitude modulation, parasitic resonances, or electronic offset voltages, for example) in frequency stabilization systems. The spectral power distribution of the oscillator waveform is modified by amplitude-modulated sidebands, and the error signal is corrected to null the induced periodic lock-point shifts. We demonstrate significant improvements to the frequency stability of standards based on cryogenic optical resonators and molecular iodine.

Theory of biphoton generation in a single-resonant optical parametric oscillator far below threshold

We present a quantum-theoretical treatment of biphoton generation in single-resonant type-II parametric down-conversion. The nonlinear medium is continuously pumped and is placed inside a cavity which is resonant for the signal field, but nonresonant for the idler deflected by an intracavity polarizing beam splitter. The intensity of the classical pump is assumed to be sufficiently low in order to yield a biphoton production rate that is small compared to the cavity loss rate. Explicit expressions are derived for the rate of biphoton generation and for the biphoton wave function. The output spectra of the signal and idler field are determined, as well as the second-order signal-idler cross-correlation function which is shown to be asymmetric with respect to the time delay. Due to frequency entanglement in the signal-idler photon pair, the idler spectrum is found to reveal the longitudinal mode structure of the cavity, even though the idler field is not resonant.

A bright continuous-wave laser source at 193 nm

This Letter reports on the realization of a highly coherent light source at 193 nm. By frequency-quadrupling an amplified diode laser, over 15 mW of laser emission could be generated using the nonlinear crystal potassium fluoro-beryllo-borate. The high stability of the setup was proven in an 80 h-measurement, and the impact of the crystal transmission on the output power was thoroughly studied. This laser source is an ideal tool for photoemission spectroscopy and reaches the power level to replace excimer lasers in metrological applications.

1.3-mW tunable and narrow-band continuous-wave light source at 191 nm

We report on the realization of a continuous-wave light source based on nonlinear interaction in KBBF at a wavelength of 191 nm. More than 1.3 mW of deep-ultraviolet power was generated in a mechanically robust setup pumped by an amplified grating stabilized diode laser. Mode hop-free tuning over 40 GHz at 191 nm could be demonstrated.

Multiplexed quantum cryptography with single InP quantum dots

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.

Single-photon generation and simultaneous observation of wave and particle properties

We describe an experiment in that generates single photons on demand and measures properties accounted to both particle and wave‐like features of light. The measurement is performed by exploiting data that are sampled simultaneously in a single experimental run.

Single Photons from Single Quantum Dots — New Light for Quantum Information Processing

In this paper, we discuss the prospects of single quantum dots for single-photon generation and their implementation in quantum information experiments. We review the characterization of quantum dot emission and, as an example, report a recently demonstrated application in a quantum cryptography protocol.