Encoding a magic state with beyond break-even fidelity

To run large-scale algorithms on a quantum computer, error-correcting codes must be able to perform a fundamental set of operations, called logic gates, while isolating the encoded information from noise1-8. We can complete a universal set of logic gates by producing special resources called magic states9-11. It is therefore important to produce high-fidelity magic states to conduct algorithms while introducing a minimal amount of noise to the computation. Here we propose and implement a scheme to prepare a magic state on a superconducting qubit array using error correction. We find that our scheme produces better magic states than those that can be prepared using the individual qubits of the device. This demonstrates a fundamental principle of fault-tolerant quantum computing12, namely, that we can use error correction to improve the quality of logic gates with noisy qubits. Moreover, we show that the yield of magic states can be increased using adaptive circuits, in which the circuit elements are changed depending on the outcome of mid-circuit measurements. This demonstrates an essential capability needed for many error-correction subroutines. We believe that our prototype will be invaluable in the future as it can reduce the number of physical qubits needed to produce high-fidelity magic states in large-scale quantum-computing architectures.

A comparison between the direct anterior and posterior approaches for total hip arthroplasty: the role of an 'Enhanced Recovery' pathway

AIMS

We assessed the difference in hospital based and early clinical outcomes between the direct anterior approach and the posterior approach in patients who undergo total hip arthroplasty (THA).

PATIENTS AND METHODS

The outcome was assessed in 448 (203 males, 245 females) consecutive patients undergoing unilateral primary THA after the implementation of an 'Enhanced Recovery' pathway. In all, 265 patients (mean age: 71 years (49 to 89); 117 males and 148 females) had surgery using the direct anterior approach (DAA) and 183 patients (mean age: 70 years (26 to 100); 86 males and 97 females) using a posterior approach. The groups were compared for age, gender, American Society of Anesthesiologists grade, body mass index, the side of the operation, pre-operative Oxford Hip Score (OHS) and attendance at 'Joint school'. Mean follow-up was 18.1 months (one to 50).

RESULTS

There was no significant difference in mean length of stay (p = 0.07), pain scores on the day of surgery, the first, second and third post-operative days (p = 0.36, 0.23, 0.25 and 0.59, respectively), the day of mobilisation (p = 0.12), the mean OHS at six and 24 months (p = 0.08, and 0.29, respectively), the incidence of infection (p = 1.0), dislocation (p = 1.0), re-operation (p = 0.21) or 28 days' re-admission (p = 0.06). Significantly more patients in the DAA group achieved a planned discharge target of three days post-operatively (68% vs 56%, p = 0.007). The rate of periprosthetic femoral fractures was significantly higher in the DAA group (p = 0.04).

CONCLUSION

We conclude that there is no difference in clinical outcomes between the DAA and the posterior approach in patients undergoing THA when an 'Enhanced Recovery' pathway is used. However, a significantly higher rate of periprosthetic femoral fractures remains a concern with the DAA, even in experienced hands.

TAKE HOME MESSAGE

Our results show that the DAA for THA is not superior to posterior approach when 'Enhanced Recovery' pathway is used. Cite this article: Bone Joint J 2016;98-B:754-60.

High threshold error correction for the surface code

An algorithm is presented for error correction in the surface code quantum memory. This is shown to correct depolarizing noise up to a threshold error rate of 18.5%, exceeding previous results and coming close to the upper bound of 18.9%. The time complexity of the algorithm is found to be polynomial with error suppression, allowing efficient error correction for codes of realistic sizes.

Bringing order through disorder: localization of errors in topological quantum memories

Anderson localization emerges in quantum systems when randomized parameters cause the exponential suppression of motion. Here we consider this phenomenon in topological models and establish its usefulness for protecting topologically encoded quantum information. For concreteness we employ the toric code. It is known that in the absence of a magnetic field this can tolerate a finite initial density of anyonic errors, but in the presence of a field anyonic quantum walks are induced and the tolerable density becomes zero. However, if the disorder inherent in the code is taken into account, we demonstrate that the induced localization allows the topological quantum memory to regain a finite critical anyon density and the memory to remain stable for arbitrarily long times. We anticipate that disorder inherent in any physical realization of topological systems will help to strengthen the fault tolerance of quantum memories.

Needle guide in shoulder arthroscopy - a technique

Distension of joint with fluid is often used to facilitate insertion of arthroscope. This may prove difficult at times in the shoulder joint, as unlike the knee, it is deeply situated, making extravasation of fluid outside the capsule, a common occurrence. This is especially true in very tight joints and is often a problem for beginners. We describe here a very effective and simple technique where a needle is used to distend the shoulder before the insertion of the arthroscope.

Neurological complications of high tibial osteotomy--the fibular osteotomy as a causative factor: a clinical and anatomical study

A clinical study of 105 upper tibial osteotomies was undertaken to investigate the incidence, pathology and outcome of perioperative neurological deficit. Motor weakness and/or sensory deficit occurred in 21 patients (20%) and in half of these the deficit was permanent. For descriptive purposes the fibula was divided into four zones. The occurrence of a neurological deficit was clearly related to the level of the fibular osteotomy. An anatomical explanation is proposed for this complication, based on cadaveric studies. Due to unacceptably high levels of complications it is recommended that the fibular osteotomy should not be performed in zones II and III (from just below the fibular head to 15 cm distal to this level).

Acute repair of injury to the anterior cruciate ligament. A long-term followup

We reviewed 30 patients at an average of 7.4 years after acute repair of the anterior cruciate ligament augmented with a loop of iliotibial tract. A noncontact twisting had been the mechanism of injury in 18 of these patients, with 28 having been injured in sports. At followup, 25 patients had not experienced symptoms of instability and 23 were able to return to unrestricted athletic activity; only 5 had been unable or unwilling to return to sporting activity at all. There had been no swelling in 23 patients; however, 17 suffered from pain on exertion. The average Lysholm score was 93.2. Joint laxity was assessed and anteroposterior tibial translation quantified with a KT-1000 arthrometer. Eighteen patients had a normal or 1+ Lachman test and 27 had an absent or 1+ pivot shift. When compared with the results of a similar study performed on this group of patients at 2 years after surgery, there had been little subjective change in knee function. However, objectively there had been significant deterioration of the anteroposterior stability of the knees at 7 years, suggesting failure of the integrity of the repaired ligament with time. An associated medial collateral ligament injury had a significant adverse effect both on the integrity of the anterior cruciate ligament repair and the incidence of postoperative stiffness.

Arthrodesis of the shoulder following brachial plexus injury

A series of 13 arthrodeses of the shoulder in adults with brachial plexus injuries have been reviewed. Using internal fixation and external splintage we aimed at a final position of 30 degrees abduction, 30 degrees flexion and 20 degrees of internal rotation. Patients were followed up for between 24 and 60 months. In only one was bony union not achieved, although the resulting fibrous union was asymptomatic. All patients had additional procedures including plexus exploration in six, Steindler procedure in two, triceps to biceps transfer in two, latissimus dorsi transfer in two, and above-elbow amputation in three. All patients stated that shoulder fusion had improved the function of their limb. Minimum range of movement was 50 degrees abduction and 40 degrees flexion. Two patients continued to complain of pain despite solid fusions. Compression arthrodesis of the shoulder is an effective method of achieving fusion and reliably improves the function in adults with brachial plexus injury.

Avulsion of the ischial apophysis. The case for open reduction and internal fixation

We report three cases of avulsion of the ischial tuberosity with marked chronic disability after delay in diagnosis and non-union of the fracture. All were treated by open reduction and internal fixation with return to full function, allowing in one case, athletic performances of Olympic standard. We also report one patient with an acute apophyseal avulsion treated by early reduction and internal fixation with restoration of full function.

Patellofemoral malalignment: a report of 68 cases treated by proximal and distal patellofemoral reconstruction

A series of 68 knees were reviewed retrospectively at an average of 56 months following surgical treatment for patellar dislocation and subluxation. Fifty-three knees in 48 patients were assessed both subjectively by questionnaire and objectively by examination, and 15 knees were evaluated by questionnaire only. All cases were treated by a proximal and distal reconstruction as described by Trillat (1964). The surgery was performed by one surgeon (MC) and reviewed independently (DW). The results were excellent in 48 knees (71 per cent), good in 12 (17 per cent) and poor in 8 (12 per cent). In no patient had there been any further episodes of dislocation. We consider this a straightforward procedure producing consistent correction of patellofemoral instability with a low morbidity.

Pes planus after tibial osteotomy

When 100 patients who had had a high tibial osteotomy for monocompartmental arthritis were reviewed, 15 were found to have evidence of neurological impairment. A severe symptomatic pes planus deformity of the ipsilateral limb had developed in 4 patients within months of surgery. Electromyographic results showed evidence of dysfunction in the territory of the posterior tibial nerve in all 4 patients, and, in 3 there was evidence of deep peroneal nerve damage. All had surgery for varus malalignment.