Uso de cânula rígida com rosca e endoscópio flexível para videolaparoscopia de acesso único em equinos em estação / Use of threaded rigid cannula and flexible endoscope for single access video laparoscopy in standing horses

Com o objetivo de promover, por meio de acesso único e com o uso de endoscópio flexível, ampla exploração da cavidade peritoneal de equinos em estação, foi concebida uma cânula laparoscópica para dar sustentação ao endoscópio e possibilitar o acesso sob visualização. O procedimento foi realizado a partir da fossa paralombar. Após pequena incisão cutânea, o endoscópio foi inserido na cânula e os músculos e o peritônio foram divulsionados mediante rotação da cânula. Logo depois da perfuração do peritônio, foi realizada a exploração da cavidade e a identificação das estruturas. Em seguida à exploração do lado ipsilateral ao acesso, realizou-se a transposição do conjunto cânula/endoscópio ventralmente à porção caudal do cólon descendente, seguida de exploração do lado contralateral. Concluída a técnica, foi executado, para fins de comparação, o mesmo procedimento por meio da fossa paralombar contralateral. Foi possível a transposição do conjunto cânula/endoscópio para o lado contralateral ao acesso em todos os procedimentos. Também foi possível a identificação da maioria das estruturas abdominais tanto pelo acesso esquerdo quanto pelo direito. A abordagem por acesso único mostrou-se viável para a exploração ampla da cavidade peritoneal, demonstrando ser uma alternativa à técnica laparoscópica convencional.(AU)

A laparoscopic cannula was designed to support a single access approach with a flexible endoscope for the wide exploration of the peritoneal cavity of standing horses. It provides support to the endoscope and allows access to the peritoneal cavity with a visual aid. This procedure was performed through the paralumbar fossa. After a small cutaneous incision, the endoscope was inserted into the cannula, and the muscles and peritoneum were divulsed through the rotation of the cannula. After the peritoneal perforation, cavity exploration and identification of structures were performed. After the exploration of the ipsilateral side of the access, the cannula/endoscope was transposed ventrally to the caudal portion of the descending colon; this was followed by the exploration of the contralateral side. Once this process was completed, the same procedure was performed through the contralateral paralumbar fossa for comparison. It was possible to transpose the cannula/endoscope set to the contralateral access side in all procedures. Further, it was possible to identify most of the abdominal structures in both the left and right access. This single access approach proved to be feasible for the extensive exploration of the peritoneal cavity, thereby indicating it can be an alternative to the conventional laparoscopic technique.(AU)

A fast quantum interface between different spin qubit encodings.

Single-spin qubits in semiconductor quantum dots hold promise for universal quantum computation with demonstrations of a high single-qubit gate fidelity above 99.9% and two-qubit gates in conjunction with a long coherence time. However, initialization and readout of a qubit is orders of magnitude slower than control, which is detrimental for implementing measurement-based protocols such as error-correcting codes. In contrast, a singlet-triplet qubit, encoded in a two-spin subspace, has the virtue of fast readout with high fidelity. Here, we present a hybrid system which benefits from the different advantages of these two distinct spin-qubit implementations. A quantum interface between the two codes is realized by electrically tunable inter-qubit exchange coupling. We demonstrate a controlled-phase gate that acts within 5.5 ns, much faster than the measured dephasing time of 211 ns. The presented hybrid architecture will be useful to settle remaining key problems with building scalable spin-based quantum computers.

Controlling the interaction of electron and nuclear spins in a tunnel-coupled quantum dot.

We present a technique for manipulating the nuclear spins and the emission polarization from a single optically active quantum dot. When the quantum dot is tunnel coupled to a Fermi sea, we have discovered a natural cycle in which an electron spin is repeatedly created with resonant optical excitation. The spontaneous emission polarization and the nuclear spin polarization exhibit a bistability. For a σ(+) pump, the emission switches from σ(+) to σ(-) at a particular detuning of the laser. Simultaneously, the nuclear spin polarization switches from positive to negative. Away from the bistability, the nuclear spin polarization can be changed continuously from negative to positive, allowing precise control via the laser wavelength.

Geometric correlations and breakdown of mesoscopic universality in spin transport.

We construct a unified semiclassical theory of charge and spin transport in chaotic ballistic and disordered diffusive mesoscopic systems with spin-orbit interaction. Neglecting dynamic effects of spin-orbit interaction, we reproduce the random matrix theory results that the spin conductance fluctuates universally around zero average. Incorporating these effects into the theory, we show that geometric correlations generate finite average spin conductances, but that they do not affect the charge conductance to leading order. The theory, which is confirmed by numerical transport calculations, allows us to investigate the entire range from the weak to the previously unexplored strong spin-orbit regime, where the spin rotation time is shorter than the momentum relaxation time.

Universal phase shift and nonexponential decay of driven single-spin oscillations.

We study, both theoretically and experimentally, driven Rabi oscillations of a single electron spin coupled to a nuclear-spin bath. Because of the long correlation time of the bath, two unusual features are observed in the oscillations. The decay follows a power law, and the oscillations are shifted in phase by a universal value of approximately pi/4. These properties are well understood from a theoretical expression that we derive here in the static limit for the nuclear bath. This improved understanding of the coupled electron-nuclear system is important for future experiments using the electron spin as a qubit.

Detection of single spin decoherence in a quantum dot via charge currents.

We consider a quantum dot attached to leads in the Coulomb blockade regime that has a spin 1 / 2 ground state. We show that, by applying an ESR field to the dot spin, the stationary current in the sequential tunneling regime exhibits a new resonance peak whose linewidth is determined by the single spin decoherence time T2. The Rabi oscillations of the dot spin are shown to induce coherent current oscillations from which T2 can be deduced in the time domain. We describe a spin inverter which can be used to pump current through a double dot via spin flips generated by ESR.

Electron and nuclear spin dynamics in antiferromagnetic molecular rings.

We study theoretically the spin dynamics of antiferromagnetic molecular rings, such as the ferric wheel Fe10. For a single nuclear or impurity spin coupled to one of the electron spins of the ring, we calculate nuclear and electronic spin correlation functions and show that nuclear magnetic resonance (NMR) and electron spin resonance (ESR) techniques can be used to detect coherent tunneling of the Néel vector in these rings. The location of the NMR/ESR resonances gives the tunnel splitting and its linewidth an upper bound on the decoherence rate of the electron spin dynamics. We illustrate the experimental feasibility of our proposal with estimates for Fe10 molecules.

Quantum computing in molecular magnets.

Shor and Grover demonstrated that a quantum computer can outperform any classical computer in factoring numbers and in searching a database by exploiting the parallelism of quantum mechanics. Whereas Shor's algorithm requires both superposition and entanglement of a many-particle system, the superposition of single-particle quantum states is sufficient for Grover's algorithm. Recently, the latter has been successfully implemented using Rydberg atoms. Here we propose an implementation of Grover's algorithm that uses molecular magnets, which are solid-state systems with a large spin; their spin eigenstates make them natural candidates for single-particle systems. We show theoretically that molecular magnets can be used to build dense and efficient memory devices based on the Grover algorithm. In particular, one single crystal can serve as a storage unit of a dynamic random access memory device. Fast electron spin resonance pulses can be used to decode and read out stored numbers of up to 105, with access times as short as 10-10 seconds. We show that our proposal should be feasible using the molecular magnets Fe8 and Mn12.

Probing entanglement and nonlocality of electrons in a double-dot via transport and noise.

Addressing the feasibility of quantum communication with electrons we consider entangled spin states of electrons in a double-dot which is weakly coupled to leads. We show that the entanglement of two electrons in the double-dot can be detected in mesoscopic transport and noise measurements. In the Coulomb blockade and cotunneling regime the singlet and triplet states lead to phase-coherent current and noise contributions of opposite signs and to Aharonov-Bohm and Berry phase oscillations. These oscillations are a genuine two-particle effect and provide a direct measure of nonlocality in entangled states. We show that the ratio of zero-frequency noise to current is equal to the electron charge.

Quantum dot as spin filter and spin memory

We consider a quantum dot in the Coulomb blockade regime weakly coupled to current leads and show that in the presence of a magnetic field it acts as an efficient spin filter (at the single-spin level), producing a spin-polarized current. Conversely, if the leads are fully spin polarized the up or the down state of the spin on the dot results in a large sequential or a small cotunneling current, and, thus, together with ESR techniques, the setup can be operated as a single-spin memory.