Single photon sources on the way to QIP attoDRY1000  attoCFM I

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 [1] 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 [2], which allowed them to perform the first 20 photon experiment leading toward quantum supremacy [3].

This measurement was realized with the attoDRY1000, and the attoCFM I.


A quantum network node and register based on silicon vacancies in diamond cryogenic positioners and cryogenic objective

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.

This measurement was realized with the ANPx101/LT - linear x-nanopositioner, the ANPz102/LT - linear z-nanopositioner, and the .


Light matter coupling in TMD monolayers and heterostructures nanopositioners for cryogenic and ambient environment
Light matter coupling in TMD monolayers and heterostructures nanopositioners for cryogenic and ambient environment

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, WSe&sub2; monolayer and MoSe&sub2;-WSe&sub2; 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 [1]. 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 [2]. 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

This measurement was realized with the ANPx101/LT - linear x-nanopositioner, the ECSx3030/Al/RT, and the ANPz102/LT - linear z-nanopositioner.


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.

This measurement was realized with the attoDRY2100, and the attoCFM IV.

Enhanced coupling of NV centre's spins and photons closed cycle cryostat attoDRY2100 and transmissionvconfocal microscope
Enhanced coupling of NV centre's spins and photons closed cycle cryostat attoDRY2100 and transmissionvconfocal microscope

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 [1] speed-up multiphoton experiment on-chip [2] and to proving the technology being ready for large-scale fabrication of identical sources [3]

This measurement was realized with the attoDRY800.

Easy to use platform for single photon experiments optical cryostat attoDRY800
Easy to use platform for single photon experiments optical cryostat attoDRY800

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.

Single photon Source at Telecom Wavelength for Quantum Computation closed cycle cryostat attoDRY1000

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.

Single Spin Magnetometry at the Nansocale AFM CFM  attoLIQUID
Single Spin Magnetometry at the Nansocale AFM CFM  attoLIQUID

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.

This measurement was realized with the attoDRY800.

A nanoscale quantum sensor at high pressures optical cryostat cryostat attoDRY800

Non equilibrium phase transitions in quantum fluids of light optical cryostat cryostat attoDRY800

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.

This measurement was realized with the attoDRY800.

Further reading:
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)

This measurement was realized with the attoCFM I, and the Low Temperature Photolithography.

Enhancing Quantum Dot Emitters by Precisely Positioned Micrometric SILs cryogenic confocal microscopy attoCFM I  closed loop scanning  cryogenic photolithography
Enhancing Quantum Dot Emitters by Precisely Positioned Micrometric SILs cryogenic confocal microscopy attoCFM I  closed loop scanning  cryogenic photolithography

Polariton dispersion in strong coupling regime optical cryostat attoDRY800

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)

This measurement was realized with the attoDRY800.

Further reading:
Related video on Youtube


Nanoscale Imaging and Control of Domain Wall Hopping with an NV Center Microscope attoLIQUID  attoAFM CFM oder CSFM

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)

This measurement was realized with the attoLIQUID1000, and the attoAFM/CFM.


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)

This measurement was realized with the attoDRY800.

Single Photon Generation with Controlled Polarization from InGaN Quantum Dots optical cryostat attoDRY800
Single Photon Generation with Controlled Polarization from InGaN Quantum Dots optical cryostat attoDRY800

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.

This measurement was realized with the attoDRY1000, and the attoCFM I.

Coupling single defects to a nanowire closed cycle cryostat attoDRY1000  cryogenic confocal microscopy attoCFM
Coupling single defects to a nanowire closed cycle cryostat attoDRY1000  cryogenic confocal microscopy attoCFM
Coupling single defects to a nanowire closed cycle cryostat attoDRY1000  cryogenic confocal microscopy attoCFM

Optical Magnetometer Reveals Lack of Conventional Meissner Effect in Iron based Superconductors attoLIQUID  attoAFM CFM oder CSFM

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.

This measurement was realized with the attoLIQUID1000, and the attoAFM/CFM.


Magneto Raman Microscopy for Probing Local Material Properties of Graphene attoRAMAN

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.


Scalable Architecture for Multi Photon Boson Sampling closed cycle cryostat attoDRY1000  cryogenic confocal microscopy attoCFM

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.

This measurement was realized with the attoDRY1000, and the attoCFM I.


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 [1]-[4]. 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. [1]
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. [1]
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. [1]

Related publications based on the attoAFM/CFM (2012-2016)
[5] A. Dréau et al., Phys. Rev. Lett. 113, 137601 (2014)
[6] A. Dréau et al., Phys. Rev. Lett. 110, 060502 (2013)
[7] L. Rondin et al., Nature communications 4, 2279 (2013)
[8] J.-P. Tetienne et al., Phys. Rev. B 87, 235436 (2013)
[9] J.-P. Tetienne et al., New J. Phys. 14, 103033 (2012)
[10] A. Dréau et al., Phys. Rev. B 85, 134107 (2012)
[11] L. Rondin et al., Appl. Phys. Lett. 100, 153118 (2012)

This measurement was realized with the attoLIQUID1000, and the attoAFM/CFM.

NV Center Based Nanomagnetometry attoLIQUID  attoAFM CFM oder CSFM
NV Center Based Nanomagnetometry attoLIQUID  attoAFM CFM oder CSFM
NV Center Based Nanomagnetometry attoLIQUID  attoAFM CFM oder CSFM
NV Center Based Nanomagnetometry attoLIQUID  attoAFM CFM oder CSFM

Collective electronic excitations of dipolar excitons closed cycle cryostat attoDRY2100  cryogenic confocal microscopy attoCFM

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.

This measurement was realized with the attoCFM III, and the attoDRY2100.


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)

This measurement was realized with the attoLIQUID1000, and the attoAFM/CFM.

Quantitative Nanoscale Vortex Imaging of Superconductors attoAFM CFM oder CSFM  attoLIQUID
Quantitative Nanoscale Vortex Imaging of Superconductors attoAFM CFM oder CSFM  attoLIQUID
Quantitative Nanoscale Vortex Imaging of Superconductors attoAFM CFM oder CSFM  attoLIQUID

Observation of Many Body Exciton States using the attoCFM I cryogenic confocal microscopy attoCFM  attoLIQUID3000

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.

This measurement was realized with the attoCFM I.


Automatic Mapping of Semiconductor QDs made with cryogenic positioner  ANP RES LT

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.

This measurement was realized with the attoCFM I, and the attoRAMAN.

Addressing Strain and Doping by Cryogenic Raman Mapping attoRAMAN
Addressing Strain and Doping by Cryogenic Raman Mapping attoRAMAN

Raman Spectroscopy on Graphene made with attoRAMAN

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 [1].

[1] 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)

This measurement was realized with the attoCFM I.


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

This measurement was realized with the attoCFM I.

Resonant Spectroscopy on a Single QD cryogenic confocal microscopy attoCFM
Resonant Spectroscopy on a Single QD cryogenic confocal microscopy attoCFM

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.

Simultaneous Reflection and Transmission cryogenic confocal microscopy attoCFM
Simultaneous Reflection and Transmission cryogenic confocal microscopy attoCFM