Frauke Izdebski

Imaging high-dimensional spatial entanglement with a camera

The light produced by parametric down-conversion shows strong spatial entanglement that leads to violations of EPR criteria for separability. Historically, such studies have been performed by scanning a single-element, single-photon detector across a detection plane. Here we show that modern electron-multiplying charge-coupled device cameras can measure correlations in both position and momentum across a multi-pixel field of view. This capability allows us to observe entanglement of around 2,500 spatial states and demonstrate Einstein–Podolsky–Rosen type correlations by more than two orders of magnitude. More generally, our work shows that cameras can lead to important new capabilities in quantum optics and quantum information science.

Solid‐State Laser, Resonant Ionization Laser Ion Source (Rilis) and Laser Beam Transport at Radioactive Ion Beam Facilities

The inception of laser resonance ionization spectroscopy and its application as a resonant ionization laser ion source (RILIS) took place merely 20 years ago with pulsed dye lasers [1–5]. By now next generation radioactive ion beam (RIB) facilities are being planned or built. Understanding and considering the unique RILIS requirements in the layout of next generation RIB facilities will allow for cost‐effective implementation of this versatile ion source. This discussion touches on laser beam transport and RILIS requirements not necessarily obvious to experts in conventional ion sources.

Optimizing the use of detector arrays for measuring intensity correlations of photon pairs

Intensity correlation measurements form the basis of many experiments based on spontaneous parametric down-conversion. In the most common situation, two single-photon avalanche diodes and coincidence electronics are used in the detection of the photon pairs, and the coincidence count distributions are measured by making use of some scanning procedure. Here we analyze the measurement of intensity correlations using multielement detector arrays. By considering the detector parameters such as the detection and noise probabilities, we found that the mean number of detected photons that maximizes the visibility of the two-photon correlations is approximately equal to the mean number of noise events in the detector array. We provide expressions predicting the strength of the measured intensity correlations as a function of the detector parameters and on the mean number of detected photons. We experimentally test our predictions by measuring far-field intensity correlations of spontaneous parametric down-conversion with an electron multiplying charge-coupled device camera, finding excellent agreement with the theoretical analysis.

Development of an epitaxial lift-off technology for II-VI nanostructures using ZnMgSSe alloys

An epitaxial lift-off technique for removing wide bandgap II-VI heterostructures from GaAs substrates has previously been demonstrated using lattice-matched MgS as the sacrificial layer. However, using MgS as an etch release layer prevents its use as a wide bandgap barrier in the rest of the structure. Here, we describe the use of the etch-resistant alloy Zn.2Mg.8S.64Se.36 which we have developed as a replacement for MgS. We demonstrate that this alloy can be grown by MBE together with MgS in heterostructures and used as a barrier for ZnSe. A ZnSe quantum well with Zn.2Mg.8S.64Se.36 barriers shows no decrease in photoluminescence intensity after the etching process but shows a shift in emission wavelength associated with the changing strain state.

Multiplexed Single-Mode Wavelength-to-Time Mapping of Multimode Light

When an optical pulse propagates along an optical fibre, different wavelengths travel at different group velocities. As a result, wavelength information is converted into arrival-time information, a process known as wavelength-to-time mapping. This phenomenon is most cleanly observed using a single-mode fibre transmission line, where spatial mode dispersion is not present, but the use of such fibres restricts possible applications. Here we demonstrate that photonic lanterns based on tapered single-mode multicore fibres provide an efficient way to couple multimode light to an array of single-photon avalanche detectors, each of which has its own time-to-digital converter for time-correlated single-photon counting. Exploiting this capability, we demonstrate the multiplexed single-mode wavelength-to-time mapping of multimode light using a multicore fibre photonic lantern with 121 single-mode cores, coupled to 121 detectors on a 32 × 32 detector array. This work paves the way to efficient multimode wavelength-to-time mapping systems with the spectral performance of single-mode systems.

Single-photon position to time multiplexing using a fiber array

A 1 x 8 fiber array is used as the front-end of a receiver system. Each channel has a different length of fiber, resulting in each channel signal arriving at the detector at a pre-determined interval relative to a constant repetitive frequency signal. We demonstrate that these eight channels can be efficiently coupled to an individual single-photon detector such that the arrival-time of a photon in each is distinguishable from the next. Thus, we demonstrate spatial position to time information exchange, resulting in a photon-counting array using a single detector. The receiver system could be implemented in numerous applications, including time-resolved photoluminescence, low-light level spectroscopy and quantum information processing.

Multiplexed wavelength-to-time conversion of multimode light (Conference Presentation)

A photonic lantern is an adiabatic guided-wave transition between a multimode waveguide and a set of single-mode cores. As such, photonic lanterns facilitate the efficient coupling of multimode light to single-mode devices, examples of which include fibre Bragg gratings and arrayed waveguide gratings. In this work, we demonstrate that photonic lanterns based on tapered multicore fibres (MCFs) provide a potentially powerful new route to efficiently couple multimode states of light to a two-dimensional array of Single Photon Avalanche Detectors (SPADs). The SPAD array consists of a 32×32 square array of pixels, each of which has its own time to digital converter (TDC) for Time Correlated Single Photon Counting (TCSPC) with a timing resolution of 55 ps. For our application, the geometry of the MCF used to fabricate the photonic lantern was chosen such that each single mode in the MCF can be mapped onto an individual SPAD pixel. Upon injecting a broad supercontinuum signal into a 290 m long MCF via a photonic lantern, wavelength-to-time mapped spectra were obtained from all modes. We believe that the techniques we report here may find applications in areas such as Raman spectroscopy, coherent LIDAR, and quantum optics.

Quantum correlations in position, momentum and intermediate bases, measured using fiber arrays

We have developed a new approach to measuring the spatial position of a single photon. Using fibers of different length, all connected to a single detector allows us to use the high timing precision of single photon avalanche diodes (SPAD) to spatially locate the photon. We have built two 8-element detector arrays to measure the full-field quantum correlations in position, momentum and intermediate bases for photon pairs produced in parametric down conversion. The strength of the position-momentum correlations is found to be an order of magnitude below the classical limit.

High-dimensional spatial entanglement observed with an electron multiplying CCD camera

Using an electron multiplying CCD camera we observe both image plane (position) and far field (momentum) correlations between photon pairs produced from spontaneous parametric down-conversion when using a 201 x 201 bi-dimensional array of pixels and a flux of around 0.02 photons/pixel. After background subtraction we characterize the strength of signal and idler correlations in both transverse dimensions by applying entanglement and EPR criteria, showing good agreement with the theoretical predictions. The application of such devices in quantum optics could have a wide range, including quantum computation with spatial degrees of freedom of single photons.

Single-photon detection in time-of-flight-depth imaging and quantum key distribution

Single-photon detectors play an increasing role in emerging application areas in quantum communication and low-light level depth imaging. The single-photon detector characteristics have a telling impact in system performance, and this presentation will examine the role of single-photon detectors in these important application areas. We will discuss the experimental system performance of GHz-clocked quantum key distribution systems focusing on issues of quantum bit error rate, net bit rate and transmission distance with different detector structures, concentrating on single-photon avalanche diode detectors, but also examining superconducting nanowire-based structures. The quantum key distribution system is designed to be environmentally robust and an examination of long-term system operation will be presented. The role of detector performance in photon-counting time-of-flight three-dimensional imaging will also be discussed. We will describe an existing experimental test bed system designed for kilometer ranging, and recent experimental results from field trials. The presentation will investigate the key trade-offs in data acquisition time, optical power levels and maximum range. In both examples, experimental demonstrations will be presented to explore future perspectives and design goals.