24 research outputs found
Diffusion properties of single FoF1-ATP synthases in a living bacterium unraveled by localization microscopy
FoF1-ATP synthases in Escherichia coli (E. coli) bacteria are membrane-bound
enzymes which use an internal proton-driven rotary double motor to catalyze the
synthesis of adenosine triphosphate (ATP). According to the 'chemiosmotic
hypothesis', a series of proton pumps generate the necessary pH difference plus
an electric potential across the bacterial plasma membrane. These proton pumps
are redox-coupled membrane enzymes which are possibly organized in
supercomplexes, as shown for the related enzymes in the mitochondrial inner
membrane. We report diffusion measurements of single fluorescent FoF1-ATP
synthases in living E. coli by localization microscopy and single enzyme
tracking to distinguish a monomeric enzyme from a supercomplex-associated form
in the bacterial membrane. For quantitative mean square displacement (MSD)
analysis, the limited size of the observation area in the membrane with a
significant membrane curvature had to be considered. The E. coli cells had a
diameter of about 500 nm and a length of about 2 to 3 \mum. Because the surface
coordinate system yielded different localization precision, we applied a
sliding observation window approach to obtain the diffusion coefficient D =
0.072 \mum2/s of FoF1-ATP synthase in living E. coli cells.Comment: 12 pages, 6 figure
Single Molecule DNA Detection with an Atomic Vapor Notch Filter
The detection of single molecules has facilitated many advances in life- and
material-sciences. Commonly, it founds on the fluorescence detection of single
molecules, which are for example attached to the structures under study. For
fluorescence microscopy and sensing the crucial parameters are the collection
and detection efficiency, such that photons can be discriminated with low
background from a labeled sample. Here we show a scheme for filtering the
excitation light in the optical detection of single stranded labeled DNA
molecules. We use the narrow-band filtering properties of a hot atomic vapor to
filter the excitation light from the emitted fluorescence of a single emitter.
The choice of atomic sodium allows for the use of fluorescent dyes, which are
common in life-science. This scheme enables efficient photon detection, and a
statistical analysis proves an enhancement of the optical signal of more than
15% in a confocal and in a wide-field configuration.Comment: 9 pages, 5 figure
Reduction of Thermomechanical Stress Using Electrically Conductive Adhesives
We compare the thermomechanical stresses in solar cell interconnections based on electrically conductive adhesives (ECA) with soldered joints by using bending experiments and finite element analysis (FEA). Additionally, the influence of an increasing number of busbars is studied. The FEA is validated by measuring the bending of cell strips after cooling down from a single-sided interconnection process. The material parameters are determined by tensile tests, microscopy and nanoindentation. The comparison of ECA and soldering shows that an elastomer with a Young's modulus of below 0.5 GPa is capable of reducing the thermomechanical stress effectively resulting in, approximately, a mean tensile stress in the ECA of 5 MPa, 110 MPa in the ribbon, and a maximum compressive stress in the silicon of 75 MPa. Increasing the number of busbars from three to five leads to a reduction in compressive stresses in the silicon and a slight increase of the peak tensile stress in the busbars
Monitoring single membrane protein dynamics in a liposome manipulated in solution by the ABELtrap
FoF1-ATP synthase is the essential membrane enzyme maintaining the cellular
level of adenosine triphosphate (ATP) and comprises two rotary motors. We
measure subunit rotation in FoF1-ATP synthase by intramolecular Foerster
resonance energy transfer (FRET) between two fluorophores at the rotor and at
the stator of the enzyme. Confocal FRET measurements of freely diffusing single
enzymes in lipid vesicles are limited to hundreds of milliseconds by the
transit times through the laser focus. We evaluate two different methods to
trap the enzyme inside the confocal volume in order to extend the observation
times. Monte Carlo simulations show that optical tweezers with low laser power
are not suitable for lipid vesicles with a diameter of 130 nm. A. E. Cohen
(Harvard) and W. E. Moerner (Stanford) have recently developed an Anti-Brownian
electrokinetic trap (ABELtrap) which is capable to apparently immobilize single
molecules, proteins, viruses or vesicles in solution. Trapping of fluorescent
particles is achieved by applying a real time, position-dependent feedback to
four electrodes in a microfluidic device. The standard deviation from a given
target position in the ABELtrap is smaller than 200 nm. We develop a
combination of the ABELtrap with confocal FRET measurements to monitor single
membrane enzyme dynamics by FRET for more than 10 seconds in solution.Comment: 12 pages, 10 figure
Coherent electrical readout of defect spins in 4H-SiC by photo-ionization at ambient conditions
Quantum technology relies on proper hardware, enabling coherent quantum state
control as well as efficient quantum state readout. In this regard,
wide-bandgap semiconductors are an emerging material platform with scalable
wafer fabrication methods, hosting several promising spin-active point defects.
Conventional readout protocols for such defect spins rely on fluorescence
detection and are limited by a low photon collection efficiency. Here, we
demonstrate a photo-electrical detection technique for electron spins of
silicon vacancy ensembles in the 4H polytype of silicon carbide (SiC). Further,
we show coherent spin state control, proving that this electrical readout
technique enables detection of coherent spin motion. Our readout works at
ambient conditions, while other electrical readout approaches are often limited
to low temperatures or high magnetic fields. Considering the excellent maturity
of SiC electronics with the outstanding coherence properties of SiC defects the
approach presented here holds promises for scalability of future SiC quantum
devices
Scalable quantum photonics with single color centers in silicon carbide
Silicon carbide is a promising platform for single photon sources, quantum bits (qubits), and nanoscale sensors based on individual color centers. Toward this goal, we develop a scalable array of nanopillars incorporating single silicon vacancy centers in 4H-SiC, readily available for efficient interfacing with free-space objective and lensed-fibers. A commercially obtained substrate is irradiated with 2 MeV electron beams to create vacancies. Subsequent lithographic process forms 800 nm tall nanopillars with 400–1400 nm diameters. We obtain high collection efficiency of up to 22 kcounts/s optical saturation rates from a single silicon vacancy center while preserving the single photon emission and the optically induced electron-spin polarization properties. Our study demonstrates silicon carbide as a readily available platform for scalable quantum photonics architecture relying on single photon sources and qubits
Readout and Control of a Single Nuclear Spin with a Metastable Electron Spin Ancilla
Electron and nuclear spins associated with point defects in insulators are promising systems for solid-state quantum technology1, 2, 3. The electron spin is usually used for readout and addressing, and nuclear spins are used as exquisite quantum bits4, 5 and memory systems3, 6. With these systems, single-shot readout of single nuclear spins5, 7 as well as entanglement4, 8, 9, aided by the electron spin, have been shown. Although the electron spin in this example is essential for readout, it usually limits the nuclear spin coherence10, leading to a quest for defects with spin-free ground states9, 11. Here, we isolate a hitherto unidentified defect in diamond and use it at room temperature to demonstrate optical spin polarization and readout with exceptionally high contrast (up to 45%), coherent manipulation of an individual excited triplet state spin, and coherent nuclear spin manipulation using the triplet electron spin as a metastable ancilla. We demonstrate nuclear magnetic resonance and Rabi oscillations of the uncoupled nuclear spin in the spin-free electronic ground state. Our study demonstrates that nuclei coupled to single metastable electron spins are useful quantum systems with long memory times, in spite of electronic relaxation processes.Engineering and Applied Science
Electrical Charge State Manipulation of Single Silicon Vacancies in a Silicon Carbide Quantum Optoelectronic Device
Colour centres with long-lived spins are established platforms for quantum
sensing and quantum information applications. Colour centres exist in different
charge states, each of them with distinct optical and spin properties.
Application to quantum technology requires the capability to access and
stabilize charge states for each specific task. Here, we investigate charge
state manipulation of individual silicon vacancies in silicon carbide, a system
which has recently shown a unique combination of long spin coherence time and
ultrastable spin-selective optical transitions. In particular, we demonstrate
charge state switching through the bias applied to the colour centre in an
integrated silicon carbide opto-electronic device. We show that the electronic
environment defined by the doping profile and the distribution of other defects
in the device plays a key role for charge state control. Our experimental
results and numerical modeling evidence that control of these complex
interactions can, under certain conditions, enhance the photon emission rate.
These findings open the way for deterministic control over the charge state of
spin-active colour centres for quantum technology and provide novel techniques
for monitoring doping profiles and voltage sensing in microscopic devices