S. Franke-arnold - Academia.edu (original) (raw)

Papers by S. Franke-arnold

Physical Review Letters, 2014

The ability to uniquely identify a quantum state is integral to quantum science, but for nonortho... more The ability to uniquely identify a quantum state is integral to quantum science, but for nonorthogonal states, quantum mechanics precludes deterministic, error-free discrimination. However, using the nondeterministic protocol of unambiguous state discrimination enables the error-free differentiation of states, at the cost of a lower frequency of success. We discriminate experimentally between nonorthogonal, highdimensional states encoded in single photons; our results range from dimension d ¼ 2 to d ¼ 14. We quantify the performance of our method by comparing the total measured error rate to the theoretical rate predicted by minimum-error state discrimination. For the chosen states, we find a lower error rate by more than 1 standard deviation for dimensions up to d ¼ 12. This method will find immediate application in high-dimensional implementations of quantum information protocols, such as quantum cryptography.

Frontiers in Optics 2010/Laser Science XXVI, 2010

Abstract: We holographically measure entangled tangles of phase singularity lines in light genera... more Abstract: We holographically measure entangled tangles of phase singularity lines in light generated via spontaneous parametric down-conversion. This type of entanglement is interesting because it is between topological features that extend over finite, macroscopic, isolated volumes. ...

Frontiers in Optics, 2006

ABSTRACT

Science, 2011

A spinning slow-light medium (ruby) crystal is used to enhance the rotation of light.

Physical Review Letters, 2004

We present a novel method for efficient sorting of photons prepared in states of orbital angular ... more We present a novel method for efficient sorting of photons prepared in states of orbital angular momentum (OAM) and angular position (ANG). A log-polar optical transform is used in combination with a holographic beam-splitting method to achieve better mode discrimination and reduced cross-talk than reported previously. Simulating this method for 7 modes, we have calculated an improved mutual information of 2.43 bits/photon and 2.29 bits/photon for OAM and ANG modes respectively. In addition, we present preliminary results from an experimental implementation of this technique. This method is expected to have important applications for high-dimensional quantum key distribution systems.

Optics Express, 2014

When linearly polarised light is transmitted through a spinning window, the plane of polarisation... more When linearly polarised light is transmitted through a spinning window, the plane of polarisation is rotated. This rotation arises through a phase change that is applied to the circularly polarised states corresponding to the spin angular momentum (SAM). Here we show an analogous effect for the orbital angular momentum (OAM), where a differential phase between the positive and negative modes (±) is observed as a rotation of the transmitted image. For normal materials, this rotation is on the order of a micro radian, but by using a slow-light medium, we show a rotation of a few degrees. We also note that, within the bounds of our experimental parameters, this rotation angle does not exceed the scale of the spatial features in the beam profile.

Optics Express, 2013

We present a technique for mapping the complete 3D spatial intensity profile of a laser beam from... more We present a technique for mapping the complete 3D spatial intensity profile of a laser beam from its fluorescence in an atomic vapour. We propagate shaped light through a rubidium vapour cell and record the resonant scattering from the side. From a single measurement we obtain a camera limited resolution of 200 x 200 transverse points and 659 longitudinal points. In constrast to invasive methods in which the camera is placed in the beam path, our method is capable of measuring patterns formed by counterpropagating laser beams. It has high resolution in all 3 dimensions, is fast and can be completely automated. The technique has applications in areas which require complex beam shapes, such as optical tweezers, atom trapping and pattern formation.

The European Physical Journal D, 2013

The European Physical Journal D - Atomic, Molecular and Optical Physics, 2003

We analyse the coherence properties of two particles trapped in a one-dimensional harmonic potent... more We analyse the coherence properties of two particles trapped in a one-dimensional harmonic potential. This simple model allows us to derive analytic expressions for the first and second order coherence functions. We investigate their properties depending on the particle nature and the temperature of the quantum gas. We find that at zero temperature non-interacting bosons and fermions show very different correlations, while they coincide for higher temperatures. We observe atom bunching for bosons and atom anti-bunching for fermions. When the effect of s-wave scattering between bosons is taken into account, we find that the range of coherence is enhanced or reduced for repulsive or attractive potentials, respectively. Strongly repelling bosons become in some way more "fermion-like" and show anti-bunching. Their first order coherence function, however, differs from that for fermions.

Physical Review Letters, 2015

Recent years have seen vast progress in the generation and detection of structured light, with po... more Recent years have seen vast progress in the generation and detection of structured light, with potential applications in high capacity optical data storage and continuous variable quantum technologies.Here we measure the transmission of structured light through cold rubidium atoms and observe regions of electromagnetically induced transparency (EIT). We use q-plates to generate a probe beam with azimuthally varyingphase and polarisation structure, and its right and left circular polarisation components provide the probe and control of an EIT transition. We observe an azimuthal modulation of the absorption profile that is dictated by thephase and polarisation structure of the probe laser. Conventional EIT systems do not exhibit phase sensitivity. We show, however, that a weak transverse magnetic field closes the EIT transitions, thereby generating phase dependent dark states which in turn lead to phase dependent transparency, in agreement with our measurements.

Biomedical Spectroscopy, Microscopy, and Imaging, 2020

When focusing a light beam at high numerical aperture, the resulting electric field profile in th... more When focusing a light beam at high numerical aperture, the resulting electric field profile in the focal plane depends on the transverse polarisation profile, as interference between different parts of the beam needs to be taken into account. It is well known that radial polarised light produces a longitudinal polarisation component and can be focused below the conventional diffraction limit for homogeneously polarised light, and azimuthally polarised light that carries one unit of angular momentum can achieve even tighter focal spots. This is of interest for example for enhancing resolution in scanning microscopy. There are numerous ways to generate such polarisation structures, however, setups can be expensive and usually rely on birefringent components, hence prohibiting broadband operation. We have recently demonstrated a passive, low-cost technique using a simple glass cone (Fresnel cone) to generate beams with structured polarisation. We show here that the polarisation structure generated by Fresnel cones focuses better than radial polarised light at all numerical apertures. Furthermore, we investigate in detail the application of polarised light structures for two-photon microscopy. Specifically we demonstrate a method that allows us to generate the desired polarisation structure at the back aperture of the microscope by pre-compensating any detrimental phase shifts using a combination of waveplates.

Communications Physics, 2018

Laguerre-Gauss beams, and more generally the orbital angular momentum of light (OAM) provide valu... more Laguerre-Gauss beams, and more generally the orbital angular momentum of light (OAM) provide valuable research tools for optical manipulation, processing, imaging and communication. High-efficiency frequency conversion of OAM is possible via four-wave mixing in rubidium vapour. Conservation of the OAM in the two pump beams determines the total OAM shared by the generated light fields at 420 nm and 5.2 μm-but not its distribution between them. Here we experimentally investigate the spiral bandwidth of the generated light modes as a function of pump OAM. A small pump OAM is transferred almost completely to the 420 nm beam. Increasing the total pump OAM broadens the OAM spectrum of the generated light, indicating OAM entanglement between the generated light fields. This clears the path to high-efficiency OAM entanglement between widely disparate wavelengths.

Structured Light and its Applications, 2008

... 5. Ren and colleagues [36] have used a similar scheme to produce hyper-entangled (entangled i... more ... 5. Ren and colleagues [36] have used a similar scheme to produce hyper-entangled (entangled in OAM, polarization and energy-time) photons. Again these states have three OAM basis states. Thus, the higher-alphabet protocols are experi-mentally realizable now. ...

New Journal of Physics, 2004

$Research paper thumbnail of Cold-atom densities of more than 10^{12} cm^{−3} in a holographically shaped dark spontaneous-force optical trap$

Physical Review A, 2013

ABSTRACT We demonstrate an atom trap geometry for ^{87}Rb which is capable of producing ultrahigh... more ABSTRACT We demonstrate an atom trap geometry for ^{87}Rb which is capable of producing ultrahigh atom densities. Reradiation forces, which usually limit high densities, can be avoided in dark spontaneous-force optical traps (dark SPOTs) by sheltering atoms from intense trapping light. Here we demonstrate a dynamic implementation of a dark SPOT, resulting in an increase in atom density by almost two orders of magnitude up to 1.3×10^{12} cm^{−3}. Holographic control of the trapping beams and dynamic switching between magneto-optical trap (MOT) and dark SPOT configuration allows us to optimize the trapping geometry. We have identified the ideal size of the dark core to be six times larger than the MOT. Our method also avoids unwanted heating so that we reach a record phase-space density for a MOT.

Proceedings of CAOL'2003. 1st International Conference on Advanced Optoelectronics and Lasers. Jontly with 1st Workshop on Precision Oscillations in Electronics and Optics (IEEE Cat. No.03EX715)

We discuss several techniques for measuring the topological charge, m, of optical vortices by uti... more We discuss several techniques for measuring the topological charge, m, of optical vortices by utilizing their m-fold rotational symmetry. Such a measurement also amounts to a measurement of the orbital angular momentum (OAM) per photon in units of hbar. The first technique involves the rotational Doppler shift, which was recently suggested as a way to measure the OAM of light beams for optical-communications purposes. The second technique involves interfering an optical vortex with the same vortex, but rotated about the vortex axis by a certain angle. This results in constructive interference for some m values, and destructive interference for other m values. This technique can, in principle, be used to measure the OAM of individual photons. The third technique uses an optical ring resonator that rotates the beam during each round trip. Such a resonator can be tuned to be resonant only for optical vortices with a given values of m. We have used such a resonator to demonstrate an angular form of the uncertainty principle.

5th International Workshop on Laser and Fiber-Optical Networks Modeling, 2003. Proceedings of LFNM 2003.

$Research paper thumbnail of Angular diffraction$

SPIE Proceedings, 2009

Angle and angular momentum are linked by a Fourier transformation. A restriction of the angular r... more Angle and angular momentum are linked by a Fourier transformation. A restriction of the angular range within an optical beam profile therefore generates orbital angular momentum (OAM) sidebands on the transmitted light. We interpret this phenomenon as angular diffraction: a mask that blocks light within one or several angular ranges is the angular analogue of a single slit or a diffraction grating, respectively. In the OAM spectra of light transmitted through angular masks we observe the typical sinc 2 envelope known from single slit diffraction, and in particular the suppression of OAM sidebands. This is the angular analogy to missing orders observed for a linear diffraction grating. Contents 5 4. Conclusions 7 Acknowledgment 8 References 8

Proceedings of SPIE - The International Society for Optical Engineering, 2007

abstract In the 1970s, Jones demonstrated a photon drag by showing that the translation of a wind... more abstract In the 1970s, Jones demonstrated a photon drag by showing that the translation of a window caused a slight displacement of a transmitted light beam. Similarly he showed that a spinning medium slightly rotated the polarization state. Rather than translating the medium, the speed of which is limited by mechanical considerations, we translate the image and measure its lateral delay with respect to a similar image that has not passed through the window. The equivalence, or lack of it, of the two frames is subtle and great care needs to ...