Topological information device operating at the Landauer limit

We propose and theoretically investigate a novel Maxwell's demon implementation based on the spin-momentum locking property of topological matter. We use nuclear spins as a memory resource which provides the advantage of scalability. We show that this topological information device can ideally operate at the Landauer limit; the heat dissipation required to erase one bit of information stored in the demon's memory approaches kBTln2. Furthermore, we demonstrate that all available energy, kBTln2 per one bit of information, can be extracted in the form of electrical work. Finally, we find that the current-voltage characteristic of topological information device satisfy the conditions of an ideal memristor.</p

Double-Fourier engineering of Josephson energy-phase relationships applied to diodes

We present a systematic method to design arbitrary energy-phase relations using parallel arms of two series Josephson tunnel junctions each. Our approach employs Fourier engineering in the energy-phase relation of each arm and the position of the arms in real space. We demonstrate our method by engineering the energy-phase relation of a near-ideal superconducting diode, which we find to be robust against the imperfections in the design parameters. Finally, we show the versatility of our approach by designing various other energy-phase relations.Comment: 13 pages, 8 figure

Current-induced nuclear spin polarization in (Bi 1-x Sb x)2 Te 3

Three-dimensional topological insulators (3DTIs) host conducting surface states, while the bulk remains insulating. These surface states are spin-momentum locked, which opens the road to spintronic applications. We investigate the hyperfine interaction between spin-momentum locked electrons and nuclear spins. A DC source-drain bias implies a nonzero electron spin polarization, which is transfered to a nonzero nuclear spin polarization via spin-flip interactions. Inversely, thermal relaxation of a nonzero nuclear spin polarization drives a charge current. This shows as an inductive current, observable at timescales comparable to the nuclear spin-flip rate. At DC timescales, the nonzero nuclear polarization is expected to affect resistance as a function of applied bias. Moreover, the additional in-plane magnetic field stemming from nuclear polarization is expected to affect phase coherence lengths. We search for signatures of current-induced nuclear polarization in the 3DTI (Bi 1-x Sb x)2 Te 3 (BST). The high nuclear spin abundancy makes this an excellent candidate material. BST thin-films are deposited by molecular beam epitaxy, which allows for tuning the position of Fermi level and Dirac point within the bulk band gap. The experiments focus on probing effects of non-zero nuclear polarization using DC signals. However, careful consideration is required to distinguish signatures of other effects, such as electron-electron interactions and Joule heating

Enhancing the excitation gap of a quantum-dot-based Kitaev chain

Connecting double quantum dots via a semiconductor-superconductor hybrid segment offers a platform for creating a two-site Kitaev chain that hosts a pair of "poor man's Majoranas" at a finely tuned sweet spot. However, the effective couplings, which are mediated by Andreev bound states in the hybrid, are generally weak in the tunneling regime. As a consequence, the excitation gap is limited in size, presenting a formidable challenge for using this platform to demonstrate non-Abelian statistics of Majoranas and realizing error-resilient topological quantum computing. In this work, we systematically study the effects of increasing the coupling between the dot and the hybrid segment. In particular, the proximity effect transforms the dot orbitals into Yu-Shiba-Rusinov states, forming a new spinless fermion basis for a Kitaev chain, and we derive a theory for their effective coupling. As the coupling strength between the dots and the hybrid segment increases, we find a significant enhancement of the excitation gap and reduced sensitivity to local perturbations. Although the hybridization of the Majorana wave function with the central Andreev bound states increases strongly with increasing coupling, the overlap of Majorana modes on the outer dots remains small, which is a prerequisite for potential qubit experiments. We discuss how the strong-coupling regime shows in experimentally accessible quantities, such as the local and non-local conductance, and provide a protocol for tuning a double-dot system into a sweet spot with a large excitation gap.Comment: 12 pages, 9 figure

Chiral adiabatic transmission protected by Fermi surface topology

We demonstrate that Andreev modes that propagate along a transparent Josephson junction have a perfect transmission at the point where three junctions meet. The chirality and the number of quantized transmission channels is determined by the topology of the Fermi surface and the vorticity of the superconducting phase differences at the trijunction. We explain this chiral adiabatic transmission (CAT) as a consequence of the adiabatic evolution of the scattering modes both in momentum and real space. We identify an effective energy barrier that guarantees quantized transmission. We expect that CAT is observable in nonlocal conductance and thermal transport measurements. Furthermore, because it does not rely on particle-hole symmetry, CAT is also possible to observe directly in metamaterials.Comment: 12 pages, 7 figure

Impact of opioid-free analgesia on pain severity and patient satisfaction after discharge from surgery: multispecialty, prospective cohort study in 25 countries

Background: Balancing opioid stewardship and the need for adequate analgesia following discharge after surgery is challenging. This study aimed to compare the outcomes for patients discharged with opioid versus opioid-free analgesia after common surgical procedures.Methods: This international, multicentre, prospective cohort study collected data from patients undergoing common acute and elective general surgical, urological, gynaecological, and orthopaedic procedures. The primary outcomes were patient-reported time in severe pain measured on a numerical analogue scale from 0 to 100% and patient-reported satisfaction with pain relief during the first week following discharge. Data were collected by in-hospital chart review and patient telephone interview 1 week after discharge.Results: The study recruited 4273 patients from 144 centres in 25 countries; 1311 patients (30.7%) were prescribed opioid analgesia at discharge. Patients reported being in severe pain for 10 (i.q.r. 1-30)% of the first week after discharge and rated satisfaction with analgesia as 90 (i.q.r. 80-100) of 100. After adjustment for confounders, opioid analgesia on discharge was independently associated with increased pain severity (risk ratio 1.52, 95% c.i. 1.31 to 1.76; P &lt; 0.001) and re-presentation to healthcare providers owing to side-effects of medication (OR 2.38, 95% c.i. 1.36 to 4.17; P = 0.004), but not with satisfaction with analgesia (beta coefficient 0.92, 95% c.i. -1.52 to 3.36; P = 0.468) compared with opioid-free analgesia. Although opioid prescribing varied greatly between high-income and low- and middle-income countries, patient-reported outcomes did not.Conclusion: Opioid analgesia prescription on surgical discharge is associated with a higher risk of re-presentation owing to side-effects of medication and increased patient-reported pain, but not with changes in patient-reported satisfaction. Opioid-free discharge analgesia should be adopted routinely

Enhancing the excitation gap of a quantum-dot-based Kitaev chain

&lt;p&gt;Code used to produce the numerical results presented in &quot;Enhancing the excitation gap of a quantum-dot-based Kitaev chain&quot; manuscript.&lt;/p&gt