Fiber alignment at mK conditions
The step from theoretical to practical quantum computing requires not only components for quantum entanglement but also a low-loss and robust network for further data distribution. The interface between superconducting processors and optical telecom networks is one of the open questions in the quantum community. A possible solution was now presented by the group of Johannes Fink from the Institute of Science and Technology Austria (Klosterneuburg, Austria). Their bidirectional and chip-scalable converter opens a way to integrate superconducting circuits into large scale optical fiber networks using a nanomechanical transducer. The precise alignment and stable connection of the optical fibre to the microwave chip at 10 mK temperatures required a stiff set of ANP101 positioners for x,y, and z movement. This new device allows using pump-powers orders of magnitudes lower than previously reported transducers which reduces optical heating and conversion noise that currently still hinders a quantum limited operation.
Extreme cross-polarization extinction
Confocal microscopy has proven to be an essential tool for studying light-matter interactions via resonant fluorescence experiments on the sub-micron scale. However, the exact mechanism behind the surprisingly strong suppression of laser light in such a configuration remained elusive.
In the framework of a PhD thesis conducted at attocube and financed through the EU’s Horizon 2020 network 4PHOTON, its origin could be attributed to the Imbert-Fedorov shift, a subtle sideways shift of a polarized beam of light when it is reflected off a smooth surface. For the precise rotation of the polarizers, an attocube piezo stepper rotator was used, whose accuracy of 15 µRad steps is essential to achieving such extreme extinction values.
Our work opens the way to a methodical design of sensitive laser resonant fluorescence microscopes with extreme background extinction, for a broad range of applications in quantum optics and solid-state physics, as well as for measuring material optical properties.
Phys. Rev. X 11, 021007
Signatures of a degenerate many-body state of excitons in van der Waals heterostacks
Condensed phases of excitons have previously been revealed by transport measurements in solid state systems with weak exciton binding, and consequently condensation temperatures below 1 K. Van der Waals heterostacks of semiconducting 2D materials are expected to host many-body phenomena at higher temperatures because of their peculiar screening properties and large exciton binding energies. The first optical exploration of such many-body phase diagrams of excitons has now been published by a collaboration of groups from Munich (Holleitner; Germany) and Münster (Wurstbauer; Germany). They used an attoDRY2100 closed cycle cryostat equipped with ANP nanopositioners to observe several criticalities in photogenerated exciton ensembles. The findings point towards a coherent many body quantum state, which survives to temperatures above 10K.
This measurement was realized with the attoDRY2100.
Phys. Rev. Research 2, 042044 (2020)
Telecom single-photon emitters in silicon
Quantum computing and quantum information processing are currently one of the hottest and best funded topics in physics. Single-photon sources are amongst the most promising candidates for photonic realizations of quantum processors, repeaters and sensors. In their recent paper, the group of Georgy Astakhov (HZDR, Dresden) managed to integrate carbon-based color centers (G center) into off-the-shelf Si wafers, resulting in bright and spectrally stable telecom single-photon sources with emission at about 1.28 µm. The experiments were conducted using an LT-APO objective with ANP nanopositioners in an attoDRY800 optical cryostat at 5.7 K. Their findings pave the way toward integrated photonic devices based on existing, scalable silicon technology combined with telecom wavelength range.
Anisotropic formation of exciton magnetic polarons in colloidal quantum dot
Colloidal nanocrystal quantum dots are - due to their reproducible and scalable fabrication process - promising candidates for many industrial applications like solar cells, LEDs and displays. Doping semiconducting colloidal nanocrystals with magnetic ions can lead to extraordinary effects, such as light-induced magnetization - aka exciton magnetic polaron (EMP). The group of Gerd Bacher (University of Duisburg-Essen, Germany) carried out temperature- and magnetic-field-dependent photoluminescence measurements on single colloidal Mn2+:CdSe/CdS quantum dots, thus shedding light on the fundamental processes that lead to EMP formation. The measurements were realized with attoCFM I in attoDRY1000 with 3D magnetic field. These findings open a new path for controlling the orientation of light-induced magnetism.
S. Lorenz et al., Nano Lett. 20, 1896 (2020)
Boosting single-photon quantum key distribution
Engineered quantum light sources emitting single photons on the push of a button are essential components for quantum communication protocols. To maximize the expected secure key and the communication distance for quantum key distribution, the group of Tobias Heindel at the Technische Universität Berlin (Berlin, Germany) developed tools to optimize the performance of quantum key distribution implemented with such engineered single-photon emitters. Exploiting two-dimensional temporal filtering, the expected secure key as well as the communication distance can be optimized. The group implemented their routine in a basic quantum key distribution testbed, comprising a quantum dot device sending single-photon pulses to a four-port receiver analysing the polarisation state of the flying qubits. The single-photon source was mounted on the cold platform of the optical cryostat attoDRY800 as the integration of the platform into an optical table offered the easiest solution for a cold spot on the optical table. Their method further allowed to demonstrate real-time security monitoring via photon-statistics, being an important step towards security certification in quantum communication.
T. Kupko et al., npj Quantum Information volume 6, 29 (2020)
Single photon sources on the way to QIP
Single-photon sources will be a fundamental building block for future quantum information devices. For advanced implementations, the photon sources must emit simultaneously high efficiency and indistinguishability photons. On the way towards an optimal solid-state based single-photon source, the group of Chaoyang Lu and Jian-Wei Pan at the University of Science and Technology of China (Shanghai, CN) presented a background-free method (two-color excitation) for generating spectrally isolated indistinguishable photons  and polarized single photons from elliptical micro-pillars. The optical measurements were performed using an attoCFM I cooled by a closed cycle attoDRY2100 cryostat. With their measurement method they demonstrated a state-of-the-art polarized single-photon efficiency of up to 60% and an indistinguishability of up to 0.975 for the micro pillar device , which allowed them to perform the first 20 photon experiment leading toward quantum supremacy .
A quantum network node and register based on silicon-vacancies in diamond
The realization of a quantum network node is a fundamental requirement for a later quantum network or even quantum internet. Such a quantum register receives or emits information without disturbing the underlying quantum state. Now, the groups of Marko Loncar and Mikhail Lukin at the Havard University (Cambridge, MA, USA) present an elementary quantum network node based on a silicon vacancy color center inside a diamond nanocavity. This optically active point defect in the diamond lattice is characterized by a self-made mK confocal microscope based on cryogenic nanopositioners and a cryogenic apochromatic objective from attocube inside a dilution cryostat. Additionally, the authors demonstrate the working principle of the node as quantum register by coupling the system to incoming optical photons, as well as a nearby nuclear spin featuring a 100ms long decoherence time. Their work marks a first step towards the realization of a first-generation quantum repeater.
C.T. Nguyen et al, Phys. Rev. B 100, 165428 (2019)
Light-matter coupling in TMD monolayers and heterostructures
Scanning optical micro-cavities have been used by two collaborating groups to study light-matter coupling phenomena in semiconductor transition metal dichalcogenide (TMD) monolayers and heterostructures. The groups of David Hunger (Karlsruher Institut für Technologie, Karlsruhe, Germany) and Alexander Högele (Ludwig-Maximillians-Universität München, Germany) explored atomically thin TMD semiconductors with scanning-cavity hyperspectral imaging at room and cryogenic temperatures. To this end, WSe2 monolayer and MoSe2-WSe2 heterobilayer were coupled to a tuneable cavity consisting of a fiber-based micro-mirror at one end and a planar micro-mirror with the sample at the other end, as sketched in figure 1. For room-temperature monolayers in strong-coupling, spatial maps of new half-matter and half-light quasiparticles – so-called exciton polaritons – were correlated to maps of exciton extinctions and fluorescence . Heterobilayers were explored in the weak-coupling regime at 4 K to demonstrate Purcell enhancement of layer-indirect excitons and to determine their oscillator strength . To ensure the required stability, the experiments employed an ECSx3030 and ANPx101 positioner for ambient and cryogenic conditions respectively, to realize the tuneable cavity and align the fiber with respect to the sample
Enhanced coupling of NV-centre's spins and photons
Reliable quantum information systems require different quantum systems combining the best features of each of them. The most flexible and universal possibilities are offered by photons as mediator between localized qubits. Therefore, an effective coupling of solid-state based qubits to an optical photon is a fundamental requirement.
Nitrogen-vacancy centres feature a long spin coherence time and their spin can be optically initialized, manipulated and detected. However, only about three percent of their photon emission are channeled into the zero phonon line. This limits the rate of indistinguishable single photons and the signal-to-noise ratio of coherent spin-photon interfaces. The group of Christoph Becher at Saarland University (Saarbrücken, Germany) designed and fabricated a tunable two-dimensional photonic crystal cavity (figure 1) and reported an enhanced emission rate of one magnitude (figure 2). The tuning of the cavity mode into resonance with the zero phonon line of the NV centre was achieved by laser-induced adsorption of residual gas provided inside the vacuum tube of the closed cycle cryostat attoDRY2100. In-situ optical detection measurements allowed to control the actual tuning process. The result of their fabrication optimization and tuning is an almost tripled signal-to-noise ratio of the optical spin read-out. According to the authors even higher signal-to-noise ratio is possible using the presented fabrication technique and experimental setup.
Easy-to-use platform for single photon experiments
The efficient generation of single, indistinguishable photons is essential for the development of optical quantum information processing. Specifically, the quest of creating single photons on-demand is limited to certain types of sources and techniques. To achieve this, the company Quandela provides optical accessories and state-of-the-art solid-state source devices emitting millions of quantum-pure photons per second.
Combining attocube's closed cycle cryostat attoDRY800 with Quandela's semiconductor quantum dot emitters guarantees a reliable and easy-to-use state-of-the-art solid-state single photon source for complex experiments and protocols.
With this robust setup it was easily possible to use the single-photon sources for on-demand generation of quantum superpositions of zero, one or two photons  speed-up multiphoton experiment on-chip  and to proving the technology being ready for large-scale fabrication of identical sources 
Single-photon Source at Telecom Wavelength for Quantum Computation
One of the most promising approaches towards devices that could act as a building block for quantum computing and quantum information technology are quantum dot based single photon sources. Some of the standing technical challenges are coupling efficiencies, lossy transmission of quantum states, and the integration of other photonic devices such as electro-optic modulators.
The group of Edo Waks at the University of Maryland (Maryland, USA) tackled these demands by developing an alignment-free fiber-coupled single photon source emitting at the telecom wavelength.
The heart of the device is a nanobeam with an embedded quantum dot attached to a tapered fiber. The photons emitted from the quantum dot are guided to the fiber, from which it can be transferred to other optical device. The characterization required a home-made all-fiber photoluminescence setup that was cooled to 4 K using the closed cycle attoDRY1000 cryostat. The observed single-photon emission was detected with a brightness of 1.5 % and a purity of 86 %. With these results the developed device is a promising candidate for quantum computing as it offers the required usability and performance.
This measurement was realized with the attoDRY1000.
Chang-Min Lee et al.; Appl. Phys. Lett. 114, 171101 (2019)
Single Spin Magnetometry at the Nansocale
Since the discovery of ferromagnetism in 2D van der Waals crystals, the community aims to study the feature quantitatively at the nanoscale. This feat was now approached by the group of Patrick Maletinsky at the University of Basel (Basel, CH).
Using their single-spin magnetometer based on electronic spins in diamond with the attoAFM/CFM, they detected the magnetization distribution of atomically thin crystals of CrI3. attocube's attoAFM/CFM offers the possibility to combine atomic force with confocal microscopy for optically detected magnetic resonance. With their technique they found the magnetization of one monolayer to be ≈ 16 µB/nm2 and addressed an open question regarding the thickness-dependence of magnetisation in CrI3.
Next to the outstanding physical result it is the technique that will add new ways of detecting and manipulating of magnetic properties at the nanoscale. According to P. Maletinsky the "single-spin magnetometry" is a "close-to ideal tool to study the physics of atomically thin 2D magnets."
This measurement was realized with the attoAFM/CFM.
A nanoscale quantum sensor at high pressures
Pressure affects phenomena ranging from the properties of planetary interiors to transitions between quantum mechanical phases. However, the enormous stress gradients generated in high pressure experimental apparatuses, such as the diamond anvil cell, limit the utility of most conventional spectroscopy techniques. To address this challenge, a novel nanoscale sensing platform was independently developed by three groups (given in alphabetic order): the Jean-Francois Roch group (Université Paris-Sud, FR), the Sen Yang group (Chinese University of Hong Kong, CN), and the Norman Yao group (University of California, Berkeley, USA). The researchers used quantum spin defects integrated into an anvil cell to detect minuscule signals under extreme pressures and temperatures with diffraction-limited spatial resolution.
For this purpose, Norman Yao and colleagues utilized the table-integrated closed cycle attoDRY800 cryostat - the ideal platform for precise and rapid temperature control of a diamond anvil cell while offering a large sample chamber and free-beam optical access. The convenience of the closed-cycle cryostat allowed the researchers to publish their results to arXiv just nine months after installation.
Non-equilibrium phase transitions in quantum fluids of light
The understanding of many quantum phenomena in solid state physics heavily relies the ability to measure the dispersion relation of the fundamental excitations of the system. In the blossoming field of cavity polariton research, this dispersion relation is directly encoded in the propagation direction of the light emitted by the sample. To decrease the background signal and, therefore, increase the detected signal's quality, thin planar samples are used to perform transmission spectroscopy measurements. The group of Martin Kroner (ETH Zürich, Swizerland) performs such spectroscopy measurements using a table integrated closed cycle cryostat, the attoDRY800, as cold platform for the sample. By allowing for free space optical access to the sample from both sides, the attoDRY800 setup is an ideal platform to carry transmission measurements. In addition, the cold platform’s compactness results in a high stability and leaves most of the optic’s table space for the optical setup.
Link to the group's webpage
Enhancing Quantum Dot Emitters by Precisely Positioned Micrometric SILs
Using interferometric closed loop scanning integrated into the attoCFM I confocal microscope for cryogenic in-situ lithography, the group of P. Michler in Stuttgart was able to optically localize quantum dots (QDs) with a unprecedented precision of 2 nm and mark them via lithography.
This procedure enables further processing and optimizing these single photon emitters to enhance light extraction. In this case, they successfully demonstrated how to precisely add hemispherical lenses directly on top of the quantum dot via 3D direct laser writing. This led to an enhancement in extraction efficiency by a factor of 2.
“Our attoCFM I LT-lithography setup is not only the best choice when it comes to stability requirements. Its closed loop scanning feature also allows us to optically pre-select quantum dots suitable for desired experiments and mark them in-situ via lithography with nanometric precision.”
Prof. Dr. Peter Michler (University of Stuttgart, Germany)
Polariton dispersion in strong coupling regime
The group of Prof. Atac Imamoglu (ETH Zurich) uses the attoDRY800 for phase contrast microscopy. The video (link below) shows the polariton dispersion in the so-called strong coupling regime, measured via white light transmission. The x-axis represents the in-plane momentum k||, the y-axis the energy E. The time evolution is given by the exciton-cavity detuning. In the inset, the corresponding spectrum at k|| = 0 is shown.
(Data courtesy of Martin Kroner; video created by Thomas Fink and Olivier Faist; Quantum Photonics Group, ETH Zurich)
Related video on Youtube
Nanoscale Imaging and Control of Domain-Wall Hopping with an NV Center Microscope
Domain walls in magnetic wires may prove useful for future spintronic devices, and hence their nanoscale characterization is an important steps towards useful applications. As demonstrated by the group of Vincent Jaques in Science, their NV center microscope based on the attoAFM/CFM allows to image domain walls in a 1 nm thick ferromagnetic nanowire with high resolution as well as jumps between pinning sites of individual domain walls. At the same time, they showed that the domain walls can be moved along the wire by inducing jumps via local heating due to a high local laser power. Since the domain walls are pinned by nearest pinning site, this allows to probe and image the pinning landscape of the sample quite efficiently.
(Images courtesy of V. Jacques, University of Montpellier, FR)
Tetienne et al ., Science 344, 1366(2014)
Single Photon Generation with Controlled Polarization from InGaN Quantum Dots
The research groups led by Prof. R. Taylor & Dr. R.A. Oliver in the UK have successfully generated single-photons with polarized light emission and predefined polarization axis at temperatures spanning from around 5 K to above 200 K using InGaN quantum dots. These quantum dots offer several advantages, such as high experimental repetition rates in the range of GHz, and for their growth as a planar structure, a single routine without complex geometrical engineering.
The emission spectra of these quantum dots were characterized using micro-photoluminescence techniques, while the samples were kept cool inside an optical cryostat equipped with attocube positioners. This table top cryostat, the attoDRY800, is able to reach temperatures ranges from below 5 K up to even above 300 K with very good thermal and vibrational stability.
The single-photons generated by these quantum dots are bright enough to allow their optical properties to be measured even above 200 K, a temperature considered to be the Peltier cooling barrier. Hence, this suggests in principle, that these quantum dots could be applied in integrated electronic circuits. And thanks to the achievable polarization control, these quantum dots are good candidates for on-chip polarization encoding in quantum cryptography.
To know more about the work done by Robert Taylor, Rachel Oliver and their research teams, please visit their websites here: https://users.physics.ox.ac.uk/~rtaylor/ and here http://www.gan.msm.cam.ac.uk/directory/oliver
(Data courtesy of R. Taylor, Oxford University)
Coupling single defects to a nanowire
Using an attoCFM I cooled by an attoDRY1000, the group of Edo Waks at the University of Maryland (Maryland, USA) succeeded to couple quantum emitters in a tungsten diselenide (WSe²) monolayer self-aligned to the surface plasmon mode of a silver nanowire. The achieved lower bound coupling efficiency was measured to be 26% ± 11% in average from the emitter into the plasmonic mode of the silver nanowire. The presented technique is versatile to construct coupled systems consisting of diverse plasmonic structures and single-defect emitters in a range of two-dimensional semiconductors. Such a coupled system could be used for applications such as ultra-fast single-photon sources, which paves a way toward super-compact plasmonic circuits.
T. Cai, et al., Nano Lett. 17, 6564 (2017)
Optical Magnetometer Reveals Lack of Conventional Meissner Effect in Iron-based Superconductors
Scientists at Ames Laboratory (US), Ruslan Prozorov and Naufer Nusran, together with graduate student Kamal Joshi succeeded to visualize spatial distribution of the magnetic induction upon penetration and expulsion of weak magnetic fields in several representative superconductors. The experimental setup is based on the Attocube AFM/CFM, a low-temperature AFM combined with a confocal microscope. Attocube’s high NA low temperature microscope objective is used to optically access the nitrogen-vacancy centers in diamond, which are essentially atomic-scale magnetic sensors.
N. M. Nusran et al., New J. Phys 20, 043010 (2018)
Magneto-Raman Microscopy for Probing Local Material Properties of Graphene
The combination of confocal Raman microscopy and magnetic fields at 4 K yields the opportunity to investigate and tune the electron-phonon interaction in graphene and few-layer graphene. In particular, excitations between Landau levels can resonantly couple to the Raman active long wavelength optical phonon (G-phonon), when their energies are matched, resulting in magneto-phonon resonances (MPRs). Such resonances at ±3.7 T are presented in the figure and highlighted by arrows. The details of the coupling depend on various material properties of the investigated graphene layer. From the MPRs, device parameters such as the electron-phonon coupling constant or the Fermi velocity of the charge carriers can be extracted. Interestingly for low charge carrier doping, the Fermi velocity shows signatures of many-body interaction effects.
This measurement was realized with the attoRAMAN.
C Neumann, et al., Nature Communications volume 6, 8429 (2015)
Scalable Architecture for Multi-Photon Boson Sampling
Research groups led by Jian-Wei Pan & Chao-Yang Lu in China and Sven Höfling in Germany & UK have successfully demonstrated the first quantum simulator based on single photons that beats early classical computers. In Nature Photonics, they report on “High-efficiency multiphoton boson sampling“, implementing 3-, 4-, and 5-boson-sampling with rates which are more than 24,000 times faster than all previous experiments, and 10-100 times faster than the first electronic computer (ENIAC) and transistorized computer (TRADIC) in human history. Their work, which was carefully prepared and accompanied by their 3 previous papers published in PRL (see below), kick starts a new era of photonic quantum technologies-going beyond proof-of-principle demonstrations and building a quantum machine to actually race against different generations of classical computers. In recognition of their achievements in quantum teleportation research, the very active and highly respected Chinese group recently also won the 2015 Physics World Breakthrough of the Year award and the 2015 State Nature Science First Class Award in China. In addition, Chao-Yang Lu was portrayed by Nature last summer as one of the “Science stars of China”. For their quantum dot experiments, his group uses three attoDRY cryostats equipped with attocube positioners, scanners and cryogenic objectives. Visit the group’s homepage for more information on their experiment.
NV-Center Based Nanomagnetometry
Given its premier mechanical and thermal stability, the attoAFM/CFM is the ideal platform for nanoscale magnetic imaging employing an AFM tip with a diamond nanocrystal that contains a single nitrogen-vacancy (NV) center -. Local magnetic fields are subsequently evaluated by measuring the Zeeman shifts of the NV defect spin sublevels. In the particular case of NV-center magnetometry, an external microwave field is emitted and tuned in frequency such that local spin resonance occurs. This condition can subsequently be detected by a decrease in photoluminescence intensity of the NV-center, referred to as ODMR (optically detected magnetic resonance). Using a Lock-in and feedback loop technique allows to maintain spin resonance while rastering the sample, allowing to record a local magnetic field map with nanometer resolution.
In this example, magnetic imaging of a hard disk sample with random bit orientation was performed in the group of V. Jacques at LPQM, ENS-Cachan, France. 
Example 1 (a,b): Quantitative imaging using ODMR based method with NV-center scanned at d1 = 250 nm above the sample. (a) Schematic of the measurement. (b) Quantitative magnetic field distribution recorded with the lockin technique (13 nm pixel size, 110 ms acquisition time per pixel). The inset shows a line-cut taken along the dashed white line in the image. 
Example 2 (c,d): All-optical method with NV center closer to the sample surface. (c) Schematic of the measurement. (d) All optical photoluminescence image (no microwave field applied) recorded with the NV-scanning probe magnetometer in tapping mode (8 nm pixel size, 20 ms acquisition time per pixel). Comparisons with simulations indicates that the tip surface distance is roughly d2 = 30 nm. Fine white dotted lines are plotted along the direction of the hard disk tracks as a guide for the eye. 
Related publications based on the attoAFM/CFM (2012-2016)
 A. Dréau et al., Phys. Rev. Lett. 113, 137601 (2014)
 A. Dréau et al., Phys. Rev. Lett. 110, 060502 (2013)
 L. Rondin et al., Nature communications 4, 2279 (2013)
 J.-P. Tetienne et al., Phys. Rev. B 87, 235436 (2013)
 J.-P. Tetienne et al., New J. Phys. 14, 103033 (2012)
 A. Dréau et al., Phys. Rev. B 85, 134107 (2012)
 L. Rondin et al., Appl. Phys. Lett. 100, 153118 (2012)
Collective electronic excitations of dipolar excitons
Photogenerated excitonic ensembles confined in coupled GaAs quantum wells are probed by a complementary approach of emission spectroscopy and resonant inelastic light scattering. The line scan of the photoluminescence energy in the image was measured at 7 K and covers the whole length of the circular trap with a diameter of 20 µm (x-axis). The inner electrode is circumvented by a ring shaped electrode at a different voltage. The gap of approx. 130 nm between the samples was created by e-beam lithography. The measurement was performed with an attoCFM III microscope inside a closed cycle attoDRY2100 cryostat.
 S. Dietl, S. Wang, D. Schuh, W. Wegscheider, J. P. Kotthaus, A. Pinczuk, A. Holleitner, and U. Wurstbauer, Phys. Rev. B 95, 085312 (2017)
 J. Repp, G. Schinner, E. Schubert, A. K. Rai, D. Reuter, A. D. Wieck, U. Wurstbauer, J. P. Kotthaus, and A. Holleitner, Applied Physics Letters 105, 241101 (2014)
Quantitative Nanoscale Vortex-Imaging of Superconductors
Understanding the microscopic mechanisms of superconductivity could be greatly facilitated by non-invasive tools that allow for quantitative imaging with nanometric resolution over a large range of temperatures and high magnetic fields. Based on the attoAFM/CFM, the group of Patrick Maletinsky (Univ. of Basel) reports on cryogenic measurements using NV center magnetometry. Their technique allows to extract quantitative data on the local magnetic field of individual superconducting vortices in YBCO with high sensitivity and spatial resolution. By determining the local London penetration depth, they find that the so called Pearl-vortex model explains the data much better and allows for fitting of additional parameters than the standard monopole model. Their experiments constitute an impressive example for how far the practical use of the NV center based magnetometry tools has already evolved.
(Images courtesy of P. Maletinsky, University of Basel, CH)
L. Thiel et al., Nature Nanotechnology 11, 677-681 (2016).
Observation of Many-Body Exciton States using the attoCFM I
Many-body interactions opens the doors to new fascinating physics such as the Fermi-edge singularity in metals, the Kondo effect in the resistance of metals with magnetic impurities and the fractional quantum Hall effect. The group of Paul M. Koenraad at the Eindhoven University of Technology (Eindhoven, NL) observed striking many-body effects in the optical spectra of a semiconductor quantum dot interacting with a degenerate electron gas using a free beam confocal microscope inside a 3He cryostat.
The image on the left shows a 3D map of the photoluminescence of a single InAs/GaAs quantum dot in a charge-tunable device. It was found that the coupling between the semiconductor quantum dot states and the continuum of the Fermi sea gives rise to new optical transitions, manifesting the formation of many-body exciton states. The experiments are an excellent proof for the stability of the attoCFM as the measurements took more than 15 hours without the need for re-alignment.
N. A. J. M. Kleemans et al., Nature Physics 6, 534 - 538 (2010)
Automatic Mapping of Semiconductor QDs
Returning to interesting sample positions has never been easier: Yves Delley from the Quantum Photonics Group (QPG) at the ETH Zurich have - based on attocube positioners with resistive encoders made for cryogenics - built a micro-photoluminescence (PL) setup and automated it to a great extent. They programmed a fully automated routine for raster-imaging a full sample of up to 4 x 4 mm2 as well as implemented an auto-focus routine. Once initiated, the positioners are moved frame-by-frame and a CCD camera takes images of the PL of their semiconductor quantum dot samples. Knowing the coordinates of all individual images, it is easy to put together a complete map of the sample (see figure ).
“Now, we have to select the interesting dots, at which we want to take a closer look”, says Yves Delley, the responsible project researcher at QPG and gags: “Yet, in order to find the shortest route between all these quantum dots, we would need a quantum computer to solve this problem.”
(Image kindly provided by Yves Delley, Quantum Photonics Group, ETH Zurich, Switzerland)
Addressing Strain and Doping by Cryogenic Raman Mapping
T. Verhagen in the Czech Academy of Sciences in Prague conducted a comprehensive study on the effects of temperature induced strain on two-layer Graphene sheets using an attoRAMANxs confocal Raman microscope. Using isotopical labelling, they can differentiate the influences of the surface on the lower and on the upper layer. A correlation analysis allows to separate strain and doping contributions to the observed Raman shifts. This detailed analysis allows to estimate temperature induced strain and doping contributions that are important when analyzing transport measurements on graphene mono- and bilayers.
T. G. A. Verhagen, et al., Phys. Rev. B 92 125437 (2015)
Raman Spectroscopy on Graphene
The figure to the left shows magneto-Raman measurements recorded at 4 K on an exfoliated single crystal of natural graphite with unprecedented spatial resolution (approx. 0.5 µm), while sweeping the magnetic field from -9 T to +9 T. The data were recorded on a single graphene flake and demonstrate the crossing of the E2g phonon energy with the electron-hole separation between the valence and conduction Landau levels.
(-N,+M) of the Dirac cone. Resonant hybridization of the E2g phonon is a specific signature of graphene flakes which display very rich Raman scattering spectra varying strongly as function of magnetic field .
 C. Faugeras et al., Phys. Rev. Lett. 107, 036807 (2011);
(attocube application labs, 2011; work in cooperation with C. Faugeras, P. Kossacki, and M. Potemski, LNCM I - Grenoble, CNRS_UJF_UPS_INSA France)
Raman Spectroscopy on Graphene made with attoRAMAN
Resonant Spectroscopy on a Single QD
Spectroscopy of semiconductor quantum dots (QDs) under resonant optical laser excitation and of other single photon emitters, such as vacancy-centers often yields more information about the emitters than more ubiquitous non-resonant excitation. However, it is a technically challenging measurement to perform. The difficulty lies within the separation of the excitation laser photons from the re-emitted and scattered photons. One way in which this can be achieved is by means of polarization suppression: in a geometry where the scattered laser photons have a well-defined polarization, they can be filtered from the detected signal facilitating the detection of resonance fluorescence (RF) of a single quantum dot or any other quantum emitter.
The attoCFM I can be upgraded with a resonant fluorescence package, which features an apochromatic performance that permits alignment free switching between off resonant PL measurements and RF. This feature is fully enabled by our novel cryogenic compatible apochromatic objectives designed to hold the focus plane at the same position on the sample independently from the photon wavelength.
The combination of high precision rotators with the flexible beam management of the confocal CFM I head leads to an easy and reproducible use for our customer. It provides extinction ratios of 107, just a factor 10 away from the world record in research labs while allowing an unprecedented flexibility of use.
The first figure shows the resonance fluorescence of a quantum dot measured with the attoCFM I equipped with the Polarization Extinction Option and a narrow band tunable laser. In order to resolve the Mollow triplet, the emission is filtered through a high resolution spectrometer. Here, the extinction ratio exceeds 106, using the low temperature near infrared apochromatic objective LT-APO\NIR.
The second figure shows the extinction ratio of the Polarization Extinction option for the attoCFM I as a function of the rotation angle of the inbuilt piezo rotator equipped with a quarter wave plate. In an angular region of 30 m° an extinction of more than 106 can be reached with a tunable narrow band diode laser (<1?pm line width).
Measurement and data by E. Kammann (1), S.H. E. Müller (1), K. Puschkarsky (2), M. Hauck (2), S. Beavan (2), A. Högele (2), and K. Karrai (1),
(1) attocube systems AG, Munich, Germany,
(2) Ludwig Maximilian Universität, Munich, Germany
Simultaneous Reflection and Transmission
The attoCFM III enables reflection and transmission measurements simultaneously. The fiber based microscope is designed to fit into any 2 inch bore-size cryostat like on of the the attoLIQUIDs, the attoDRY1000 or DRY2100.
The presented images of reflection (left) and transmission (right) are taken from a Vanadium rhomb-structure on a glass substrate with a layer thickness of 50 nm and a periodicity of 5 µm.
(attocube application labs 2007)
This measurement was realized with the attoCFM III.