90 research outputs found
Fast Hole Tunneling Times in Germanium Hut Wires Probed by Single-Shot Reflectometry
Heavy holes confined in quantum dots are predicted to be promising candidates
for the realization of spin qubits with long coherence times. Here we focus on
such heavy-hole states confined in Germanium hut wires. By tuning the growth
density of the latter we can realize a T-like structure between two neighboring
wires. Such a structure allows the realization of a charge sensor, which is
electrostatically and tunnel coupled to a quantum dot, with charge-transfer
signals as high as 0.3e. By integrating the T-like structure into a
radio-frequency reflectometry setup, single-shot measurements allowing the
extraction of hole tunneling times are performed. The extracted tunneling times
of less than 10s are attributed to the small effective mass of Ge
heavy-hole states and pave the way towards projective spin readout
measurements
Single-shot readout of hole spins in Ge
The strong atomistic spin orbit coupling of holes makes single-shot spin
readout measurements difficult because it reduces the spin lifetimes. By
integrating the charge sensor into a high bandwidth radio-frequency
reflectometry setup we were able to demonstrate single-shot readout of a
germanium quantum dot hole spin and measure the spin lifetime. Hole spin
relaxation times of about 90 s at 500\,mT are reported. By analysing
separately the spin-to-charge conversion and charge readout fidelities insight
into the processes limiting the visibilities of hole spins has been obtained.
The analyses suggest that very high hole visibilities are feasible at realistic
experimental conditions underlying the potential of hole spins for the
realization of viable qubit devices
PtSi Clustering In Silicon Probed by Transport Spectroscopy
Metal silicides formed by means of thermal annealing processes are employed
as contact materials in microelectronics. Control of the structure of
silicide/silicon interfaces becomes a critical issue when the device
characteristic size is reduced below a few tens of nanometers. Here we report
on silicide clustering occurring within the channel of PtSi/Si/PtSi Schottky
barrier transistors. This phenomenon is investigated through atomistic
simulations and low-temperature resonant tunneling spectroscopy. Our results
provide evidence for the segregation of a PtSi cluster with a diameter of a few
nanometers from the silicide contact. The cluster acts as metallic quantum dot
giving rise to distinct signatures of quantum transport through its discrete
energy states
Ge hole spin qubit
Holes confined in quantum dots have gained considerable interest in the past
few years due to their potential as spin qubits. Here we demonstrate double
quantum dot devices in Ge hut wires. Low temperature transport measurements
reveal Pauli spin blockade. We demonstrate electric-dipole spin resonance by
applying a radio frequency electric field to one of the electrodes defining the
double quantum dot. Next, we induce coherent hole spin oscillations by varying
the duration of the microwave burst. Rabi oscillations with frequencies
reaching 140MHz are observed. Finally, Ramsey experiments reveal dephasing
times of 130ns. The reported results emphasize the potential of Ge as a
platform for fast and scalable hole spin qubit devices
Facial asymmetry and midsagittal plane definition in 3D: A bias-free, automated method.
Symmetry is a fundamental biological concept in all living organisms. It is related to a variety of physical and social traits ranging from genetic background integrity and developmental stability to the perception of physical appearance. Within this context, the study of human facial asymmetry carries a unique significance. Here, we validated an efficient method to assess 3D facial surface symmetry by best-fit approximating the original surface to its mirrored one. Following this step, the midsagittal plane of the face was automatically defined at the midpoints of the contralateral corresponding vertices of the superimposed models and colour coded distance maps were constructed. The method was tested by two operators using facial models of different surface size. The results show that the midsagittal plane definition was highly reproducible (maximum error < 0.1 mm or°) and remained robust for different extents of the facial surface model. The symmetry assessments were valid (differences between corresponding bilateral measurement areas < 0.1 mm), highly reproducible (error < 0.01 mm), and were modified by the extent of the initial surface model. The present landmark-free, automated method to assess facial asymmetry and define the midsagittal plane of the face is accurate, objective, easily applicable, comprehensible and cost effective
Damage Control Surgery for Liver Trauma
The liver is one of the most commonly injured organs of the abdomen after major trauma and may lead to the extravasation of major amounts of blood. Damage control surgery (DCS) as a concept exists for over one hundred years but has been more widely optimized and implemented over the past few decades. Minimizing the time from the trauma scene to the hospital and recognizing the patterns of injury and the “lethal triad” (acidosis, hypothermia, coagulopathy) is vital to understand which patients will benefit the most from DCS. Immediate patient resuscitation, massive blood transfusion, and taking the patient to the operating room as soon as possible are the critical initial steps that have been associated with improved outcomes. Bleeding and contamination control should be the priority in this first exploratory laparotomy, while the patient should be transferred to the intensive care unit postoperatively with only temporary abdominal wall closure. Once the patient is stabilized, a second operation should be performed where an anatomic liver resection or other more major procedures may take place, along with permanent closure of the abdominal wall
Recommended from our members
Zero-Bias Anomaly in a Nanowire Quantum Dot Coupled to Superconductors
We studied the low-energy states of spin-1/2 quantum dots defined in InAs/InP nanowires and coupled to aluminum superconducting leads. By varying the superconducting gap with a magnetic field B we investigated the transition from strong coupling to weak-coupling , where is the Kondo temperature. Below the critical field, we observe a persisting zero-bias Kondo resonance that vanishes only for low B or higher temperatures, leaving the room to more robust subgap structures at bias voltages between and . For strong and approximately symmetric tunnel couplings, a Josephson supercurrent is observed in addition to the Kondo peak. We ascribe the coexistence of a Kondo resonance and a superconducting gap to a significant density of intragap quasiparticle states, and the finite-bias subgap structures to tunneling through Shiba states. Our results, supported by numerical calculations, own relevance also in relation to tunnel-spectroscopy experiments aiming at the observation of Majorana fermions in hybrid nanostructures.Chemistry and Chemical Biolog
Heavy hole states in Germanium hut wires
Hole spins have gained considerable interest in the past few years due to
their potential for fast electrically controlled qubits. Here, we study holes
confined in Ge hut wires, a so far unexplored type of nanostructure. Low
temperature magnetotransport measurements reveal a large anisotropy between the
in-plane and out-of-plane g-factors of up to 18. Numerical simulations verify
that this large anisotropy originates from a confined wave function which is of
heavy hole character. A light hole admixture of less than 1% is estimated for
the states of lowest energy, leading to a surprisingly large reduction of the
out-of-plane g-factors. However, this tiny light hole contribution does not
influence the spin lifetimes, which are expected to be very long, even in non
isotopically purified samples
Zero field splitting of heavy-hole states in quantum dots
Using inelastic cotunneling spectroscopy we observe a zero field splitting within the spin triplet manifold of Ge hut wire quantum dots. The states with spin ±1 in the confinement direction are energetically favored by up to 55 μeV compared to the spin 0 triplet state because of the strong spin–orbit coupling. The reported effect should be observable in a broad class of strongly confined hole quantum-dot systems and might need to be considered when operating hole spin qubits
- …