Evidence for the utility of quantum computing before fault tolerance.

Quantum computing promises to offer substantial speed-ups over its classical counterpart for certain problems. However, the greatest impediment to realizing its full potential is noise that is inherent to these systems. The widely accepted solution to this challenge is the implementation of fault-tolerant quantum circuits, which is out of reach for current processors. Here we report experiments on a noisy 127-qubit processor and demonstrate the measurement of accurate expectation values for circuit volumes at a scale beyond brute-force classical computation. We argue that this represents evidence for the utility of quantum computing in a pre-fault-tolerant era. These experimental results are enabled by advances in the coherence and calibration of a superconducting processor at this scale and the ability to characterize1 and controllably manipulate noise across such a large device. We establish the accuracy of the measured expectation values by comparing them with the output of exactly verifiable circuits. In the regime of strong entanglement, the quantum computer provides correct results for which leading classical approximations such as pure-state-based 1D (matrix product states, MPS) and 2D (isometric tensor network states, isoTNS) tensor network methods2,3 break down. These experiments demonstrate a foundational tool for the realization of near-term quantum applications4,5.

High-performance superconducting quantum processors via laser annealing of transmon qubits.

Scaling the number of qubits while maintaining high-fidelity quantum gates remains a key challenge for quantum computing. Presently, superconducting quantum processors with >50 qubits are actively available. For these systems, fixed-frequency transmons are attractive because of their long coherence and noise immunity. However, scaling fixed-frequency architectures proves challenging because of precise relative frequency requirements. Here, we use laser annealing to selectively tune transmon qubits into desired frequency patterns. Statistics over hundreds of annealed qubits demonstrate an empirical tuning precision of 18.5 MHz, with no measurable impact on qubit coherence. We quantify gate error statistics on a tuned 65-qubit processor, with median two-qubit gate fidelity of 98.7%. Baseline tuning statistics yield a frequency-equivalent resistance precision of 4.7 MHz, sufficient for high-yield scaling beyond 103 qubit levels. Moving forward, we anticipate selective laser annealing to play a central role in scaling fixed-frequency architectures.

Transsphenoidal microsurgery.

Transsphenoidal microsurgery is a well-established neurosurgical procedure that has become the standard of care in the management of the majority of pituitary tumors and a select group of other sellar lesions. The safety of the procedure depends on the surgeon's adherence to certain anatomic concepts. Foremost among these concepts is the necessity of preserving the integrity of the arachnoid membrane covering the tumor dome and avoiding vascular injuries in the cavernous sinus. The objective of this article is to demonstrate the sequential steps of a transsphenoidal microsurgical procedure for the removal of a pituitary tumor in light of the anatomic concepts discussed, with the goal of preventing complications and achieving the best possible outcome.

Imaging the cerebrovascular tree in the cadaveric head for planning surgical strategy.

OBJECTIVE: The objective of the study was to identify whether an integration of cadaveric dissections with preoperative imaging information may enable a better understanding of pathological anatomy, especially vascular lesions, and thus allow for greater precision in surgical planning. METHODS: We selected a computed tomographic contrast agent and experimentally determined the proportion of it that could mix compatibly with the silicone compound. The resultant mixture was injected into the cerebrovascular systems of six fresh human cadaveric heads. The specimens underwent computed tomography for the purpose of digital virtual exposures in parallel with laboratory dissections performed on these specimens. RESULTS: The 1:8 ratio of contrast agent to silicone rubber was determined to be appropriate for both computed tomography and subsequent laboratory dissection of the specimens. The blood vessels in computed tomographic scans demonstrated a higher attenuation than surrounding soft tissues. The opacity consistency of the injected vessels was a critical parameter for a clear three-dimensional rendering of the vascular structures in the natural surroundings of the skull base. Static and dynamic three-dimensional images of the cadaveric vascular tree were obtained as viewed through surgical corridors of various skull base approaches. CONCLUSION: We demonstrated a new cadaveric preparation model for imaging and dissection. This model allows for static and dynamic three-dimensional examination of the surgical anatomy from a neurosurgeon's perspective. It may facilitate the study of cerebrovascular system morphology/pathology in relation to the skull base as a tool for surgical planning.

Performance of monolayer graphene nanomechanical resonators with electrical readout.

The enormous stiffness and low density of graphene make it an ideal material for nanoelectromechanical applications. Here, we demonstrate the fabrication and electrical readout of monolayer graphene resonators, and test their response to changes in mass and temperature. The devices show resonances in the megahertz range, and the strong dependence of resonant frequency on applied gate voltage can be fitted to a membrane model to yield the mass density and built-in strain of the graphene. Following the removal and addition of mass, changes in both density and strain are observed, indicating that adsorbates impart tension to the graphene. On cooling, the frequency increases, and the shift rate can be used to measure the unusual negative thermal expansion coefficient of graphene. The quality factor increases with decreasing temperature, reaching approximately 1 x 10(4) at 5 K. By establishing many of the basic attributes of monolayer graphene resonators, the groundwork for applications of these devices, including high-sensitivity mass detectors, is put in place.

Determination of the young's modulus of structurally defined carbon nanotubes.

We have combined optical characterization with a magnetic actuation technique to measure the stiffness of single-walled carbon nanotubes of defined crystal structure. The measured stiffnesses correspond to an average Young's modulus of E = 0.97 +/- 0.16 TPa. For the structures investigated, no dependence on the nanotube chiral index was observed within the indicated experimental accuracy.

Suboccipital retrosigmoid approach for removal of vestibular schwannomas: facial nerve function and hearing preservation.

In this report, we discuss the pertinent bony, arachnoid, and neurovascular anatomy of vestibular schwannomas that has an impact on the surgical technique for removal of these tumors, with the goal of facial nerve and hearing preservation. The surgical technique is described in detail starting with anesthesia, positioning, and neurophysiological monitoring and continuing with the exposure, technical nuances of tumor removal, hemostasis, and closure. Positive prognostic factors for hearing preservation are also highlighted.

Recurrence of pediatric cerebral arteriovenous malformations after angiographically documented resection.

Angiographically confirmed surgical resection is believed to be the 'gold standard' for cure in the treatment of intracranial arteriovenous malformations (AVMs). However, rare exceptions of recurrent AVMs have been documented. We are aware of 11 reported cases of recurrent AVMs in which complete resection of the initial lesion was confirmed by postoperative angiography. Eight of these cases were in the pediatric population. In this report, we present 2 additional cases of such recurrent lesions, review the clinical and scientific literature on this rare phenomenon and provide suggested management guidelines.