30 research outputs found
Controlling spin-orbit interactions in silicon quantum dots using magnetic field direction
Silicon quantum dots are considered an excellent platform for spin qubits,
partly due to their weak spin-orbit interaction. However, the sharp interfaces
in the heterostructures induce a small but significant spin-orbit interaction
which degrade the performance of the qubits or, when understood and controlled,
could be used as a powerful resource. To understand how to control this
interaction we build a detailed profile of the spin-orbit interaction of a
silicon metal-oxide-semiconductor double quantum dot system. We probe the
derivative of the Stark shift, -factor and -factor difference for two
single-electron quantum dot qubits as a function of external magnetic field and
find that they are dominated by spin-orbit interactions originating from the
vector potential, consistent with recent theoretical predictions. Conversely,
by populating the double dot with two electrons we probe the mixing of singlet
and spin-polarized triplet states during electron tunneling, which we conclude
is dominated by momentum-term spin-orbit interactions that varies from 1.85 MHz
up to 27.5 MHz depending on the magnetic field orientation. Finally, we exploit
the tunability of the derivative of the Stark shift of one of the dots to
reduce its sensitivity to electric noise and observe an 80 % increase in
. We conclude that the tuning of the spin-orbit interaction will be
crucial for scalable quantum computing in silicon and that the optimal setting
will depend on the exact mode of qubit operations used
Current experimental upper bounds on spacetime diffusion
A consistent theory describing the dynamics of quantum systems interacting on
a classical space-time was recently put forward by Oppenheim et al..[1, 2].
Quantum states may retain their coherence, at the cost of some amount of
stochasticity of the spacetime metric, characterized by a spacetime diffusion
parameter. Here, we report existing experimental upper bounds on such
space-time diffusion, based on a review of several types of experiments with
very low force noise over a broad range of test masses from single atoms to
several kilograms. We find an upper bound at least 15 orders of magnitude lower
as compared to the initial bounds for explicit models presented by Oppenheimn
et al. The results presented here provide a path forward for future experiments
that can help evaluate classical-quantum theoriesComment: 8 pages, 1 figure, 1 tabl
Optomechanical quantum teleportation
Quantum teleportation, the faithful transfer of an unknown input state onto a
remote quantum system, is a key component in long distance quantum
communication protocols and distributed quantum computing. At the same time,
high frequency nano-optomechanical systems hold great promise as nodes in a
future quantum network, operating on-chip at low-loss optical telecom
wavelengths with long mechanical lifetimes. Recent demonstrations include
entanglement between two resonators, a quantum memory and microwave to optics
transduction. Despite these successes, quantum teleportation of an optical
input state onto a long-lived optomechanical memory is an outstanding
challenge. Here we demonstrate quantum teleportation of a polarization-encoded
optical input state onto the joint state of a pair of nanomechanical
resonators. Our protocol also allows for the first time to store and retrieve
an arbitrary qubit state onto a dual-rail encoded optomechanical quantum
memory. This work demonstrates the full functionality of a single quantum
repeater node, and presents a key milestone towards applications of
optomechanical systems as quantum network nodes
Gate-based single-shot readout of spins in silicon
Electron spins in silicon quantum dots provide a promising route towards realizing the large number of coupled qubits required for a useful quantum processor 1–7 . For the implementation of quantum algorithms and error detection 8–10 , qubit measurements are ideally performed in a single shot, which is presently achieved using on-chip charge sensors, capacitively coupled to the quantum dots 11 . However, as the number of qubits is increased, this approach becomes impractical due to the footprint and complexity of the charge sensors, combined with the required proximity to the quantum dots 12 . Alternatively, the spin state can be measured directly by detecting the complex impedance of spin-dependent electron tunnelling between quantum dots 13–15 . This can be achieved using radiofrequency reflectometry on a single gate electrode defining the quantum dot itself 15–19 , significantly reducing the gate count and architectural complexity, but thus far it has not been possible to achieve single-shot spin readout using this technique. Here, we detect single electron tunnelling in a double quantum dot and demonstrate that gate-based sensing can be used to read out the electron spin state in a single shot, with an average readout fidelity of 73%. The result demonstrates a key step towards the readout of many spin qubits in parallel, using a compact gate design that will be needed for a large-scale semiconductor quantum processor
Increased Mortality in SDHB but Not in SDHD Pathogenic Variant Carriers
Germline mutations in succinate dehydrogenase subunit B and D (SDHB and SDHD) are
predisposed to hereditary paraganglioma (PGL) and pheochromocytoma (PHEO). The phenotype of
pathogenic variants varies according to the causative gene. In this retrospective study, we estimate
the mortality of a nationwide cohort of SDHB variant carriers and that of a large cohort of SDHD
variant carriers and compare it to the mortality of a matched cohort of the general Dutch population.
A total of 192 SDHB variant carriers and 232 SDHD variant carriers were included in this study.
The Standard Mortality Ratio (SMR) for SDHB mutation carriers was 1.89, increasing to 2.88 in carriers
affected by PGL. For SDHD variant carriers the SMR was 0.93 and 1.06 in affected carriers. Compared
to the general population, mortality seems to be increased in SDHB variant carriers, especially in
those affected by PGL. In SDHD variant carriers, the mortality is comparable to that of the general Dutch population, even if they are affected by PGL. This insight emphasizes the significance of
DNA-testing in all PGL and PHEO patients, since different clinical risks may warrant gene-specific
management strategies
High potential for CH4 emission mitigation from oil infrastructure in one of EU's major production regions
Ambitious methane (CH4) emission mitigation represents one of the most effective opportunities to slow the rate of global warming over the next decades. The oil and gas (O&G) sector is a significant source of methane emissions, with technically feasible and cost-effective emission mitigation options. Romania, a key O&G producer within the EU, with the second highest reported annual CH4 emissions from the energy sector in the year 2020 (Greenhouse Gas Inventory Data - Comparison by Category, 2022), can play an important role towards the EU's emission reduction targets. In this study, we quantify CH4 emissions from onshore oil production sites in Romania at source and facility level using a combination of ground- and drone-based measurement techniques. Measured emissions were characterized by heavily skewed distributions, with 10% of the sites accounting for more than 70% of total emissions. Integrating the results from all site-level quantifications with different approaches, we derive a central estimate of 5.4 kg h-1 per site of CH4 (3.6 %-8.4 %, 95% confidence interval) for oil production sites. This estimate represents the third highest when compared to measurementbased estimates of similar facilities from other production regions. Based on our results, we estimate a total of 120 kt CH4 yr-1 (range: 79-180 kt yr-1) from oil production sites in our studied areas in Romania. This is approximately 2.5 times higher than the reported emissions from the entire Romanian oil production sector for 2020. Based on the source-level characterization, up to three-quarters of the detected emissions from oil production sites are related to operational venting. Our results suggest that O&G production infrastructure in Romania holds a massive mitigation potential, specifically by implementing measures to capture the gas and minimize operational venting and leaks