Sweet-spot operation of a germanium hole spin qubit with highly anisotropic noise sensitivity

Spin qubits defined by valence band hole states are attractive for quantum information processing due to their inherent coupling to electric fields, enabling fast and scalable qubit control. Heavy holes in germanium are particularly promising, with recent demonstrations of fast and high-fidelity qubit operations. However, the mechanisms and anisotropies that underlie qubit driving and decoherence remain mostly unclear. Here we report the highly anisotropic heavy-hole g-tensor and its dependence on electric fields, revealing how qubit driving and decoherence originate from electric modulations of the g-tensor. Furthermore, we confirm the predicted Ising-type hyperfine interaction and show that qubit coherence is ultimately limited by 1/f charge noise, where f is the frequency. Finally, operating the qubit at low magnetic field, we measure a dephasing time ofT 2 *  = 17.6 μs, maintaining single-qubit gate fidelities well above 99% even at elevated temperatures of T > 1 K. This understanding of qubit driving and decoherence mechanisms is key towards realizing scalable and highly coherent hole qubit arrays.

Phase-Driving Hole Spin Qubits

The spin-orbit interaction in spin qubits enables spin-flip transitions, resulting in Rabi oscillations when an external microwave field is resonant with the qubit frequency. Here, we introduce an alternative driving mechanism mediated by the strong spin-orbit interactions in hole spin qubits, where a far-detuned oscillating field couples to the qubit phase. Phase-driving at radio frequencies, orders of magnitude slower than the microwave qubit frequency, induces highly nontrivial spin dynamics, violating the Rabi resonance condition. By using a qubit integrated in a silicon fin field-effect transistor, we demonstrate a controllable suppression of resonant Rabi oscillations and their revivals at tunable sidebands. These sidebands enable alternative qubit control schemes using global fields and local far-detuned pulses, facilitating the design of dense large-scale qubit architectures with local qubit addressability. Phase-driving also decouples Rabi oscillations from noise, an effect due to a gapped Floquet spectrum and can enable Floquet engineering high-fidelity gates in future quantum processors.

Small Charging Energies and g-Factor Anisotropy in PbTe Quantum Dots

PbTe is a semiconductor with promising properties for topological quantum computing applications. Here, we characterize electron quantum dots in PbTe nanowires selectively grown on InP. Charge stability diagrams at zero magnetic field reveal large even-odd spacing between Coulomb blockade peaks, charging energies below 140 μeV and Kondo peaks in odd Coulomb diamonds. We attribute the large even-odd spacing to the large dielectric constant and small effective electron mass of PbTe. By studying the Zeeman-induced level and Kondo splitting in finite magnetic fields, we extract the electron g-factor as a function of magnetic field direction. We find the g-factor tensor to be highly anisotropic with principal g-factors ranging from 0.9 to 22.4 and to depend on the electronic configuration of the devices. These results indicate strong Rashba spin-orbit interaction in our PbTe quantum dots.

Out-of-equilibrium phonons in gated superconducting switches

Recent experiments have suggested that superconductivity in metallic nanowires can be suppressed by the application of modest gate voltages. The source of this gate action has been debated and either attributed to an electric-field effect or to small leakage currents. Here we show that the suppression of superconductivity in titanium nitride nanowires on silicon substrates does not depend on the presence or absence of an electric field at the nanowire, but requires a current of high-energy electrons. The suppression is most efficient when electrons are injected into the nanowire, but similar results are obtained when electrons are passed between two remote electrodes. This is explained by the decay of high-energy electrons into phonons, which propagate through the substrate and affect superconductivity in the nanowire by generating quasiparticles. By studying the switching probability distribution of the nanowire, we also show that high-energy electron emission leads to a much broader phonon energy distribution compared with the case where superconductivity is suppressed by Joule heating near the nanowire.

Ultrahigh vacuum packaging and surface cleaning for quantum devices

We describe design, implementation, and performance of an ultra-high vacuum (UHV) package for superconducting qubit chips or other surface sensitive quantum devices. The UHV loading procedure allows for annealing, ultra-violet light irradiation, ion milling, and surface passivation of quantum devices before sealing them into a measurement package. The package retains vacuum during the transfer to cryogenic temperatures by active pumping with a titanium getter layer. We characterize the treatment capabilities of the system and present measurements of flux tunable qubits with an average T₁ = 84 µs and T₂ ^echo=134μs after vacuum-loading these samples into a bottom loading dilution refrigerator in the UHV-package.

Abstract P1-18-01: Incidence of hypocalcemia in patients with metastatic breast cancer under treatment with denosumab: A non-inferiority phase III trial assessing prevention of symptomatic skeletal events (SSE) with denosumab administered every 4 weeks versus every 12 weeks: SAKK 96/12 (REDUSE)

Background

Monthly Denosumab (DN) has shown superiority over zoledronic acid (ZA) in delaying skeletal related events. Randomized trials have shown that ZA given every 12 weeks (q12w) is non-inferior to ZA given every 4 weeks (q4w). The primary endpoint of the REDUSE-trial is non-inferiority for SSE for DN q12w versus q4w. Here we present early data for hypocalcemia (HC), a secondary endpoint.

Methods

Patients with bone metastasis from breast cancer (BC) not pretreated with DN or Bisphosphonates were randomized 1:1 to receive DN q4w (Arm A) versus q12w (Arm B) after a 3-month induction phase with q4w therapy for both arms. All patients received vitamin D 400 U (VitD) and calcium (Ca) 500 mg daily. Measurement of albumin-corrected serum-Ca was mandatory before each DN injection (HC defined as <2.0 mmol/l like in CTCAE V4.0). This safety interim analysis was performed after 3.5 years of accrual. Patients who received at least 1 dose of DN were considered evaluable.

Results

351 BC-patients are currently included (177 in Arm A, 174 in Arm B). HC was the most common side effect with a rate of 20% in the first 16 weeks (during the induction phase with DN q4w for both Arms) and 19% afterwards (combined for Arms A and B). After week 16 HC-prevalence differed between the two arms: while HC was present in 25% in Arm A (q4w), the rate was only 12% in Arm B (q12w). Grade 3 HC (i.e. corrected Ca 1.5 - 1.74 mmol/l or hospitalisation indicated) was rare (0.3%), no grade 4 HC occurred. After 1 year of treatment, the rate of HC compared to the induction phase had decreased in Arm B but not in Arm A (A: 25%, B: 12%). Since HC improved in more patients in Arm B than in Arm A whereas it worsened in more patients in Arm A than in Arm B, a remarkable difference for HC resulted between the two arms.

Rates of hypocalcemia and change of severity after week 16* Arm A (N = 177)Arm B (N = 174)Rates of hypocalcemian (%)n (%)Patients with hypocalcemia at any time49 (28%)46 (26%)Patients with hypocalcemia after week 16*44 (25%)21 (12%)   Change in hypocalcemia grade after week 16*for the 49 patients with hypocalcemiafor the 46 patients with hypocalcemiaWorsening25 (51%)8 (17%)Stable10 (20%)9 (20%)Improving14 (29%)29 (63%)   *week 16: i.e. the time where the schedules of DN begin to differ between Arm A and Arm BArm A: DN q4w for weeks 1 - 12 and likewise thereafter / Arm B: DN q4w for weeks 1 - 12 and q12w thereafter

Conclusions

In our trial up to 20% of all BC patients treated with DN experienced HC in the q4w induction phase despite mandatory supplementation of VitD and Ca. This rate is considerably higher than the numbers reported in the registration trials of DN (where it was 5.5% for BC). After the induction phase, HC is markedly reduced in the q12w arm compared to q4w. This suggests that DN given q12w has a more favorable long-term safety profile in terms of HC compared to DN q4w.

Citation Format: Müller A, Templeton AJ, Hayoz S, Hawle H, Hasler-Strub U, Schwitter M, Pestalozzi BC, Pagani O, Bützberger P, Wehrhahn T, Rauch D, Inauen R, Betticher D, Zaman K, Bodmer A, Popescu RA, Rothschild S, Schardt J, Borner M, Fuhrer A, Schär C, Gillessen S, von Moos R, For the Swiss Group for Clinical Cancer Research (SAKK). Incidence of hypocalcemia in patients with metastatic breast cancer under treatment with denosumab: A non-inferiority phase III trial assessing prevention of symptomatic skeletal events (SSE) with denosumab administered every 4 weeks versus every 12 weeks: SAKK 96/12 (REDUSE) [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-18-01.

CMOS platform for atomic-scale device fabrication

Controlled atomic scale fabrication based on scanning probe patterning or surface assembly typically involves a complex process flow, stringent requirements for an ultra-high vacuum environment, long fabrication times and, consequently, limited throughput and device yield. We demonstrate a device platform that overcomes these limitations by integrating scanning-probe based dopant device fabrication with a CMOS-compatible process flow. Silicon on insulator substrates are used featuring a reconstructed Si(001):H surface that is protected by a capping chip and has pre-implanted contacts ready for scanning tunneling microscope (STM) patterning. Processing in ultra-high vacuum is thereby reduced to a few critical steps. Subsequent reintegration of the samples into the CMOS process flow opens the door to successful application of STM fabricated dopant devices in more complex device architectures. Full functionality of this approach is demonstrated with magnetotransport measurements on degenerately doped STM patterned Si:P nanowires up to room temperature.

Superconducting Grid-Bus Surface Code Architecture for Hole-Spin Qubits

We present a scalable hybrid architecture for the 2D surface code combining superconducting resonators and hole-spin qubits in nanowires with tunable direct Rashba spin-orbit coupling. The backbone of this architecture is a square lattice of capacitively coupled coplanar waveguide resonators each of which hosts a nanowire hole-spin qubit. Both the frequency of the qubits and their coupling to the microwave field are tunable by a static electric field applied via the resonator center pin. In the dispersive regime, an entangling two-qubit gate can be realized via a third order process, whereby a virtual photon in one resonator is created by a first qubit, coherently transferred to a neighboring resonator, and absorbed by a second qubit in that resonator. Numerical simulations with state-of-the-art coherence times yield gate fidelities approaching the 99% fault tolerance threshold.

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 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 compared with those for pure heavy holes. Given this tiny light-hole contribution, the spin lifetimes are expected to be very long, even in isotopically nonpurified samples.

Atomic structure of Mn wires on Si(001) resolved by scanning tunneling microscopy

At submonolayer coverage, Mn forms atomic wires on the Si(001) surface oriented perpendicular to the underlying Si dimer rows. While many other elements form symmetric dimer wires at room temperature, we show that Mn wires have an asymmetric appearance and pin the Si dimers nearby. We find that an atomic configuration with a Mn trimer unit cell can explain these observations as due to the interplay between the Si dimer buckling phase near the wire and the orientation of the Mn trimer. We study the resulting four wire configurations in detail using high-resolution scanning tunneling microscopy (STM) imaging and compare our findings with the STM images simulated by density functional theory.

Breakdown of the Korringa law of nuclear spin relaxation in metallic GaAs

We present nuclear spin relaxation measurements in GaAs epilayers using a new pump-probe technique in all-electrical, lateral spin-valve devices. The measured T(1) times agree very well with NMR data available for T>1 K. However, the nuclear spin relaxation rate clearly deviates from the well-established Korringa law expected in metallic samples and follows a sublinear temperature dependence T(1)(-1) is proportional to T(0.6) for 0.1 K≤T≤10 K. Further, we investigate nuclear spin inhomogeneities.

Probing confined phonon modes by transport through a nanowire double quantum dot

Strong radial confinement in semiconductor nanowires leads to modified electronic and phononic energy spectra. We analyze the current response to the interplay between quantum confinement effects of the electron and phonon systems in a gate-defined double quantum dot in a semiconductor nanowire. We show that current spectroscopy of inelastic transitions between the two quantum dots can be used as an experimental probe of the confined phonon environment. The resulting discrete peak structure in the measurements is explained by theoretical modeling of the confined phonon mode spectrum, where the piezoelectric coupling is of crucial importance.

Atomic-scale, all epitaxial in-plane gated donor quantum dot in silicon

Nanoscale control of doping profiles in semiconductor devices is becoming of critical importance as channel length and pitch in metal oxide semiconductor field effect transistors (MOSFETs) continue to shrink toward a few nanometers. Scanning tunneling microscope (STM) directed self-assembly of dopants is currently the only proven method for fabricating atomically precise electronic devices in silicon. To date this technology has realized individual components of a complete device with a major obstacle being the ability to electrically gate devices. Here we demonstrate a fully functional multiterminal quantum dot device with integrated donor based in-plane gates epitaxially assembled on a single atomic plane of a silicon (001) surface. We show that such in-plane regions of highly doped silicon can be used to gate nanostructures resulting in highly stable Coulomb blockade (CB) oscillations in a donor-based quantum dot. In particular, we compare the use of these all epitaxial in-plane gates with conventional surface gates and find superior stability of the former. These results show that in the absence of the randomizing influences of interface and surface defects the electronic stability of dots in silicon can be comparable or better than that of quantum dots defined in other material systems. We anticipate our experiments will open the door for controlled scaling of silicon devices toward the single donor limit.

Spin states of holes in Ge/Si nanowire quantum dots

We investigate tunable hole quantum dots defined by surface gating Ge/Si core-shell nanowire heterostructures. In single level Coulomb-blockade transport measurements at low temperatures spin doublets are found, which become sequentially filled by holes. Magnetotransport measurements allow us to extract a g factor g approximately 2 close to the value of a free spin-1/2 particle in the case of the smallest dot. In less confined quantum dots smaller g factor values are observed. This indicates a lifting of the expected strong spin-orbit interaction effects in the valence band for holes confined in small enough quantum dots. By comparing the excitation spectrum with the addition spectrum we tentatively identify a hole exchange interaction strength chi approximately 130 microeV.

Electrical properties of self-assembled branched InAs nanowire junctions

We investigate electrical properties of self-assembled branched InAs nanowires. The branched nanowires are catalytically grown using chemical beam epitaxy, and three-terminal nanoelectronic devices are fabricated from the branched nanowires using electron-beam lithography. We demonstrate that, in difference from conventional macroscopic junctions, the fabricated self-assembled nanowire junction devices exhibit tunable nonlinear electrical characteristics and a signature of ballistic electron transport. As an example of applications, we demonstrate that the self-assembled three-terminal nanowire junctions can be used to implement the functions of frequency mixing, multiplication, and phase-difference detection of input electrical signals at room temperature. Our results suggest a wide range of potential applications of branched semiconductor nanostructures in nanoelectronics.

Direct measurement of the spin-orbit interaction in a two-electron InAs nanowire quantum dot

We demonstrate control of the electron number down to the last electron in tunable few-electron quantum dots defined in catalytically grown InAs nanowires. Using low temperature transport spectroscopy in the Coulomb blockade regime, we propose a method to directly determine the magnitude of the spin-orbit interaction in a two-electron artificial atom with strong spin-orbit coupling. Because of a large effective g factor |g(*)|=8+/-1, the transition from a singlet S to a triplet T+ ground state with increasing magnetic field is dominated by the Zeeman energy rather than by orbital effects. We find that the spin-orbit coupling mixes the T+ and S states and thus induces an avoided crossing with magnitude Delta(SO)=0.25+/-0.05 meV. This allows us to calculate the spin-orbit length lambda(SO) approximately 127 nm in such systems using a simple model.

Few electron double quantum dots in InAs/InP nanowire heterostructures

We report on fabrication of double quantum dots in catalytically grown InAs/InP nanowire heterostructures. In the few-electron regime, starting with both dots empty, our low-temperature transport measurements reveal a clear shell structure for sequential charging of the larger of the two dots with up to 12 electrons. The resonant current through the double dot is found to depend on the orbital coupling between states of different radial symmetry. The charging energies are well described by a capacitance model if next-neighbor capacitances are taken into account.

Tunable double quantum dots in InAs nanowires defined by local gate electrodes

We report on low-temperature transport measurements on single and double quantum dots defined using local gates to electrostatically deplete InAs nanowires grown by chemical beam epitaxy. This technique allows us to define multiple quantum dots along a semiconducting nanowire and tune the coupling between them.

Spatially resolved manipulation of single electrons in quantum dots using a scanned probe

The scanning metallic tip of a scanning force microscope was coupled capacitively to electrons confined in a lithographically defined gate-tunable quantum dot at a temperature of 300 mK. Single electrons were made to hop on or off the dot by moving the tip or by changing the tip bias voltage owing to the Coulomb-blockade effect. Spatial images of conductance resonances map the interaction potential between the tip and individual electronic quantum dot states. Under certain conditions this interaction is found to contain a tip-voltage induced and a tip-voltage-independent contribution.

Kondo effect in a many-electron quantum ring

The Kondo effect is investigated in a many-electron quantum ring as a function of the magnetic field. For fields applied perpendicular to the plane of the ring a modulation of the Kondo effect with the Aharonov-Bohm period is observed. This effect is discussed in terms of the energy spectrum of the ring and the parametrically changing tunnel coupling. In addition, we use gate voltages to modify the ground-state spin of the ring. The observed splitting of the Kondo-related zero-bias anomaly in this configuration is tuned with an in-plane magnetic field.

Magnetic-field-dependent transmission phase of a double-dot system in a quantum ring

The Aharonov-Bohm effect is measured in a four-terminal open ring geometry. Two quantum dots are embedded in the structure, one in each of the two interfering paths. The number of electrons in the two dots can be controlled independently. The transmission phase is measured as electrons are added to or taken away from the individual quantum dots. Although the measured phase shifts are in qualitative agreement with theoretical predictions, the phase evolution exhibits unexpected dependence on the magnetic field. Phase lapses are found only in certain ranges of the magnetic field.

Singlet-triplet transition tuned by asymmetric gate voltages in a quantum ring

Wave-function and interaction effects in the addition spectrum of a Coulomb-blockaded many-electron quantum ring are investigated as a function of asymmetrically applied gate voltages and magnetic field. Hartree and exchange contributions to the interaction are quantitatively evaluated at a crossing between states extended around the ring and states which are more localized in one arm of the ring. A gate tunable singlet-triplet transition of the two uppermost levels of this many-electron ring is identified at zero magnetic field.

Energy spectra of quantum rings

Quantum mechanical experiments in ring geometries have long fascinated physicists. Open rings connected to leads, for example, allow the observation of the Aharonov-Bohm effect, one of the best examples of quantum mechanical phase coherence. The phase coherence of electrons travelling through a quantum dot embedded in one arm of an open ring has also been demonstrated. The energy spectra of closed rings have only recently been studied by optical spectroscopy. The prediction that they allow persistent current has been explored in various experiments. Here we report magnetotransport experiments on closed rings in the Coulomb blockade regime. Our experiments show that a microscopic understanding of energy levels, so far limited to few-electron quantum dots, can be extended to a many-electron system. A semiclassical interpretation of our results indicates that electron motion in the rings is governed by regular rather than chaotic motion, an unexplored regime in many-electron quantum dots. This opens a way to experiments where even more complex structures can be investigated at a quantum mechanical level.

[New treatment possibilities for skin changes with the CO2 laser in head and neck surgery]

Laser treatment of various skin changes has become common clinical practice in recent years. Due to its physical properties, the CO2 laser is particularly well suited for cutting and ablating tissue. The high absorption of its wavelength in water (lambda = 10600 nm) is responsible for its low penetration depth in biological tissue. Shortening the exposure time minimizes thermal side effects, such as carbonization and coagulation. This effect can be lessened with the Silk Touch scanner, since the focussed laser beam is moved over a defined area by rapidly rotating mirrors. This enables a controlled and reliable removal of various dermal lesions. Particularly well-suited for treatment hypertrophic scars, post-acne scarring, perioral and periorbital wrinkles, rhinophymas and benign neoplasms including verruca vulgaris. Cosmetically favorable reepithelialization of the treated skin surfaces occurs within a very short time after treatment. Periorbital resurfacing and correction of a rhinophyma are used as examples of dermal treatment with the CO2 laser and the Silk Touch scanner.

[Current status of laser surgery in the area of the soft palate and adjoining regions]

The amount of different clinically available lasers is increasing. The ENT surgeon can therefore use the best laser for the planned operation. As the resources of the hospital do not increase with the laser technology, a decision has to be made whether in addition to the universal CO2-laser other types must be acquired and which type is best. This paper presents the characteristics and typical tissue interactions of several lasers for the area of the soft palate. Typical operative examples are shown, e.g. partial resection of the soft palate in patients with bronchopathy and sleep apnoea syndrome, tonsillectomy, tonsillotomy and adenotomy in adults.