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.
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."
Exceptional Drift Stability: Cryogenic Wide-field Microscopy
When dealing with optical microscopy at low temperatures, one pre-requisite of paramount importance is the spatial stability: scarce optical signals such as those from single photon sources often imply long acquisition times, and hence require conditions as stable as possible over extended measurement periods. Temperature fluctuations and gradients, combined with mismatched thermal expansion coefficients among the parts, can jeopardize the acquisition of images over a range of temperatures or longer periods of time.
The LT-APO configuration of the attoDRY800 with cold apochromatic objectives has been expressly designed in order to optimize the stability performance. Overall, this minimizes thermal drifts significantly compared to optics sitting at room temperature - be it in vacuum or outside of the cryostat:
· no measurable drift over 40 h at base temperature, and up to 30 K
· smaller by almost a factor of 20 compared to warm objectives over the full temperature range
Also, vibrations are absolutely no concern since there is no measurable difference between cryocooler ON and OFF configuration even at ultimate resolution.
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.
S. Hsieh et al., Imaging stress and magnetism at high pressures using a nanoscale quantum sensor, arXiv:1812.08796 (2018)
M. Lesik, et al., Magnetic measurements on micron-size samples under high pressure using designed NV centers, arXiv:1812.09894 (2018)
K. Yau Yip et al., Quantum sensing of local magnetic field texture in strongly correlated electron systems under extreme conditions, arXiv:1812.10116 (2018)
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).
Material Composition and Strain Analysis
Often for material structure analysis, invasive techniques such as e.g. neutron scattering or energy dispersive X-ray spectroscopy inside a focussed ion beam microscope are used to obtain information. Unfortunately, such techniques may generate permanent perturbations to the sample under study.
Researchers at University of Sheffield have developed a modified optically detected Nuclear Magnetic Resonance (ODNMR) technique for low temperature analysis, which allows for structural analysis of strained quantum dots. NMR is a non-invasive technique, which extracts information using the fundamental properties of nucleus for different materials.
The new method is sensitive enough to probe individual strained nanostructures with only 100000 quadrupole nuclear spins. Therefore, this innovative technique proved to be an important non-invasive spectroscopy method for structural analysis especially of strained nanostructures as it requires no special preparation of the sample.
Dynamic nuclear polarisation in GaAs/AlGaAs dots observed at 4 K
In this note, nuclear spin effects are studied in individual quantum dots pumped by circularly polarised excitation using an attoCFM I. Spin is transferred from optically generated electrons to the system of about 10.000 nuclear spins. The effect of nuclear spin polarisation on the electron spin can be described in terms of effective nuclear magnetic field (also referred to as Overhauser field). Optically generated Overhauser fields of the order of several Tesla are observed localised in a single quantum dot of 4 x 20 x 20 nm3 in size.
Room temperature platform for ODMR
After decades of evolution in magnetic imaging, combining the sensitivity needed to detect single electron or nuclear spins with a spatial resolution of a few nanometers may soon become current state-of-the-art instrumentation: nitrogen vacancy (NV) nanomagnetometry based on the principle of optically detected magnetic resonance (ODMR) is commonly considered the most promising candidate to achieve this goal. While there is significant scientific activity to both reliably prepare appropriate nanodiamonds with tailored NV center characteristics and to attach them onto AFM tips, attocube is complementing these efforts by providing an ideal platform for ODMR: the attoCSFM combines a high-NA confocal microscope for optical detection in transmission with a cantilever based atomic force microscope, completely built from non-magnetic materials.
The sample environment can be adjusted from ambient pressure to low vacuum (≈1 mbar), providing integrated temperature control and subsequent drifts to less than 10 nm/h. Precise relative positioning of the sample, AFM tip, high NA objective, and an optional permanent magnet is enabled via 10 degrees of freedom provided by nanopositioning stages and scanners (positioning ranges 15 mm x 15 mm x 15 mm, scan ranges 20 µm x 20 µm x 7 µm).
This measurement was realized with the Combined Atomic Force & Confocal Microscope.
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)
Cryogen-free confocal measurements on a single quantum dot
The data to the left show photon anti-bunching experiments performed on a single quantum dot. The optical insert was cooled down by a closed cycle attoDRY1000 cryostat. Without any special effort the customer observed that the dot luminescence intensity remains constant within 14% over 10 hours.
(The data was generously provided by Benito Alén Millán, Molecular Beam Epitaxy group at the Instituto de Microelectrónica de Madrid, Spain)
Photocurrent Measurements on Graphene Devices
Spatially resolved photocurrent measurements on a graphene field-effect device in the QHE regime are presented to study the distribution of Landau levels and its relation with macroscopic transport characteristics. The exceptional stability and the ease of use of the attoCFM microscope greatly facilitated these measurements and allowed for measuring working devices in magnetic fields from -9 T to +9 T.
Confocal Microscopy on Quantum Dots at 50 mK
A customized attoCFM II module was implemented into a dilution refrigerator for the detailed investigation of quantum dots in an ultra-low temperature environment and magnetic fields of up to 7 T. The figure shows differential transmission measurements on a InAs quantum dot embedded in a GaAs matrix at 50 mK. The pronounced deviation from the lineshape as expected from the quantum confined Stark effect is due to many-particle interactions.
C. Latta et al., Nature 474, 627 (2011)
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)
Vectorial Scanning Force Microscopy Using a Nanowire Sensor
Using a GaAs/AlGaAs nanowire and its two distinct flexural modes the group of Martino Poggio in Basel was able to detect lateral 2D forces in a novel type of low temperature AFM system. An XYZ set of attocube’s ultra stable ANPx311/HL/LT/UHV cryogentic positioners helped in positioning the nanowire in the focus point of an interferometer detecting its motion. A second 3D set of attocube positioners was used to position and image the sample. Detection of both eigenmodes is possible due to their distinct resonance frequency. Interaction with an in-plane field lead to a rotation of the eigenmodes the angle of which yields the force field.
This measurement was realized with the ANPx311/HL/LT/UHV - linear x-nanopositioner.
Nanomanipulation of 1-D nanostructures using ECSx3030 positioners inside an electron microscope
The group of Horacio Espinosa at Northwestern University has employed attocube‘s ECS3030 positioners (controlled by an ECC100 piezo-controller) to accomplish nanometer precise manipulation of various nanotubes inside a SEM chamber. Once a nanowire is picked up, the manipulator is used to position it on top of a MEMS device for testing elastic strength as well as for four-point electrical measurements.
Cavity Enhanced Raman Microscopy
level signals remain intrinsically small. Recently Th. Hümmer et al from the group of Prof. Hänsch achieved a more than sixfold amplification by putting the sample inside a tiny cavity. The cavity formed by the sample and a micro mirror on the tip of an optical fiber (1) can be scanned by a set of attocube’s ECSx3030 positioners to obtain images with close to optical resolution. The micro cavity is adjusted with some tens of pm resolution using another ECS positioner and an additional piezo. The signal is enhanced due to the Purcell effect stemming from the enhanced photon lifetime in a small cavity volume (2).
The group around Dr. Hunger at the LMU Munich applied the new method to some carbon nanotubes leading to clear pictures showing (3) the extinction cross-section and (4) the Raman signal of the G’ mode. “The cavity amplifies both the Raman scattering process as well as absorption from the sample. This allows one to combine ultrasensitive absorption microscopy with Raman imaging within a single measurement.”, explains Dr. Hunger. The group is confident to improve the method further boosting the signal enhancement by several orders of magnitude in the future.
(*Pictures are under Creative Commons Attribution 4.0 international license)
Optical absorption on a single semiconductor quantum dot with a magnetic field applied in Voigt geometry
The modular design of the attoCFM III represents a highly flexible and versatile system for high resolution transmission spectroscopy. In these experiments, the setup has been modified to accommodate an inverted geometry. A special confocal objective was designed that redirects the incoming light by 90° to impinge onto the sample perpendicular to the externally applied magnetic field, i.e. in Voigt geometry.
Electronic state hybridisation at magnetic field and 4K
Photoluminescence intensity from charged excitons at cryogenic temperatures: the data shows the spectra of a singly (left), doubly (center) and triply (right graph) charged InAs quantum dot as a function of magnetic field (red or dark corresponds to high intensity). The measurements are recorded at cryogenic temperature using the attoCFM II with a magnetic field applied perpendicular to the quantum dot plane. The gate voltage (Vg) is applied between a gate and a back contact in order to tune the dot charge via coulomb blockade.
Instead of showing a diamagnetic shift, the triply charged state suddenly couples to the 2D electron gas - a coherent hybridization - as can be understood from the 1/B periodicity. These states have no analogue in atomic physics but can be described by a new version of the Anderson model, a model that describes interactions between localized and extended states.
K. Karrai et. al., Nature 427, 135-138 (2004)
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
Resonance Fluorescence Spectroscopy
In this Application Note, we present resonance fluorescence spectroscopy measurements on a semiconductor quantum dot measured with our attoCFM I. We successfully employed the new polarization extinction upgrade in combination with our new infrared ranged, apochromatic performance, low-temperature objectives. Spectral filtering of the emission reveals the Mollow triplet.
Ultra-Low Drift with the Photonic Probe Station
The integration of the Photonic Probe Station into the attoDRY800 cryostat allows for characterization of photonic structures in a temperature range from 4 K up to 320 K.
The stability of the light injection and detection is outstanding: ultra low drift of the transmitted signal intensity in the range of only a few percent in a period of several days is detected. A typical 4 h measurement is presented. The experiment schematics is shown below.
This measurement was realized with the Cryogenic Photonic Probe Station.
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.
3 color spot high resolution alignment
The figure to the left shows a superposition of the focused spots of three CFM channels at 4 K with the following key features:
- Spots alignment resolution ±15 nm
- Absolute positioning (contouring) error: 12 nm @ 1 µm/s
- Long term drift less than 10 nm/h
(attocube application labs, 2011)
attoAFM/CFM in Toploading Insert
The presented data was taken with a mk-compatible version of the attoAFM/CFM mounted on a toploading insert of a Leiden Cryogenics closed-cycle dilution refrigerator. The sample temperature was 60 mK during an AFM scan with a speed of 400nm/s. The images nicely demonstrates that the delicate microscope works very well even under these extreme conditions.
Remarkable Long Term Stability
Long term drift measurements recorded at cryogenic temperatures on a single quantum object using all three channels of the attoCFM. The position drifts during 20 hours of measurement time account for less than ±10 nm/hr in X and Y direction. Image size is 1.25 x 1.25 µm2.
(attocube application labs, 2011)