Dynamics of magnetization at infinite temperature in a Heisenberg spin chain

Understanding universal aspects of quantum dynamics is an unresolved problem in statistical mechanics. In particular, the spin dynamics of the one-dimensional Heisenberg model were conjectured as to belong to the Kardar-Parisi-Zhang (KPZ) universality class based on the scaling of the infinite-temperature spin-spin correlation function. In a chain of 46 superconducting qubits, we studied the probability distribution of the magnetization transferred across the chain's center, [Formula: see text]. The first two moments of [Formula: see text] show superdiffusive behavior, a hallmark of KPZ universality. However, the third and fourth moments ruled out the KPZ conjecture and allow for evaluating other theories. Our results highlight the importance of studying higher moments in determining dynamic universality classes and provide insights into universal behavior in quantum systems.

Stable quantum-correlated many-body states through engineered dissipation

Engineered dissipative reservoirs have the potential to steer many-body quantum systems toward correlated steady states useful for quantum simulation of high-temperature superconductivity or quantum magnetism. Using up to 49 superconducting qubits, we prepared low-energy states of the transverse-field Ising model through coupling to dissipative auxiliary qubits. In one dimension, we observed long-range quantum correlations and a ground-state fidelity of 0.86 for 18 qubits at the critical point. In two dimensions, we found mutual information that extends beyond nearest neighbors. Lastly, by coupling the system to auxiliaries emulating reservoirs with different chemical potentials, we explored transport in the quantum Heisenberg model. Our results establish engineered dissipation as a scalable alternative to unitary evolution for preparing entangled many-body states on noisy quantum processors.

Measurement-induced entanglement and teleportation on a noisy quantum processor

Measurement has a special role in quantum theory1: by collapsing the wavefunction, it can enable phenomena such as teleportation2 and thereby alter the 'arrow of time' that constrains unitary evolution. When integrated in many-body dynamics, measurements can lead to emergent patterns of quantum information in space-time3-10 that go beyond the established paradigms for characterizing phases, either in or out of equilibrium11-13. For present-day noisy intermediate-scale quantum (NISQ) processors14, the experimental realization of such physics can be problematic because of hardware limitations and the stochastic nature of quantum measurement. Here we address these experimental challenges and study measurement-induced quantum information phases on up to 70 superconducting qubits. By leveraging the interchangeability of space and time, we use a duality mapping9,15-17 to avoid mid-circuit measurement and access different manifestations of the underlying phases, from entanglement scaling3,4 to measurement-induced teleportation18. We obtain finite-sized signatures of a phase transition with a decoding protocol that correlates the experimental measurement with classical simulation data. The phases display remarkably different sensitivity to noise, and we use this disparity to turn an inherent hardware limitation into a useful diagnostic. Our work demonstrates an approach to realizing measurement-induced physics at scales that are at the limits of current NISQ processors.

Non-Abelian braiding of graph vertices in a superconducting processor

Indistinguishability of particles is a fundamental principle of quantum mechanics¹. For all elementary and quasiparticles observed to date-including fermions, bosons and Abelian anyons-this principle guarantees that the braiding of identical particles leaves the system unchanged^2,3. However, in two spatial dimensions, an intriguing possibility exists: braiding of non-Abelian anyons causes rotations in a space of topologically degenerate wavefunctions^4-8. Hence, it can change the observables of the system without violating the principle of indistinguishability. Despite the well-developed mathematical description of non-Abelian anyons and numerous theoretical proposals^9-22, the experimental observation of their exchange statistics has remained elusive for decades. Controllable many-body quantum states generated on quantum processors offer another path for exploring these fundamental phenomena. Whereas efforts on conventional solid-state platforms typically involve Hamiltonian dynamics of quasiparticles, superconducting quantum processors allow for directly manipulating the many-body wavefunction by means of unitary gates. Building on predictions that stabilizer codes can host projective non-Abelian Ising anyons^9,10, we implement a generalized stabilizer code and unitary protocol²³ to create and braid them. This allows us to experimentally verify the fusion rules of the anyons and braid them to realize their statistics. We then study the prospect of using the anyons for quantum computation and use braiding to create an entangled state of anyons encoding three logical qubits. Our work provides new insights about non-Abelian braiding and, through the future inclusion of error correction to achieve topological protection, could open a path towards fault-tolerant quantum computing.

Formation of robust bound states of interacting microwave photons

Systems of correlated particles appear in many fields of modern science and represent some of the most intractable computational problems in nature. The computational challenge in these systems arises when interactions become comparable to other energy scales, which makes the state of each particle depend on all other particles1. The lack of general solutions for the three-body problem and acceptable theory for strongly correlated electrons shows that our understanding of correlated systems fades when the particle number or the interaction strength increases. One of the hallmarks of interacting systems is the formation of multiparticle bound states2-9. Here we develop a high-fidelity parameterizable fSim gate and implement the periodic quantum circuit of the spin-½ XXZ model in a ring of 24 superconducting qubits. We study the propagation of these excitations and observe their bound nature for up to five photons. We devise a phase-sensitive method for constructing the few-body spectrum of the bound states and extract their pseudo-charge by introducing a synthetic flux. By introducing interactions between the ring and additional qubits, we observe an unexpected resilience of the bound states to integrability breaking. This finding goes against the idea that bound states in non-integrable systems are unstable when their energies overlap with the continuum spectrum. Our work provides experimental evidence for bound states of interacting photons and discovers their stability beyond the integrability limit.

Noise-resilient edge modes on a chain of superconducting qubits

Inherent symmetry of a quantum system may protect its otherwise fragile states. Leveraging such protection requires testing its robustness against uncontrolled environmental interactions. Using 47 superconducting qubits, we implement the one-dimensional kicked Ising model, which exhibits nonlocal Majorana edge modes (MEMs) with ℤ 2 parity symmetry. We find that any multiqubit Pauli operator overlapping with the MEMs exhibits a uniform late-time decay rate comparable to single-qubit relaxation rates, irrespective of its size or composition. This characteristic allows us to accurately reconstruct the exponentially localized spatial profiles of the MEMs. Furthermore, the MEMs are found to be resilient against certain symmetry-breaking noise owing to a prethermalization mechanism. Our work elucidates the complex interplay between noise and symmetry-protected edge modes in a solid-state environment.

Realizing topologically ordered states on a quantum processor

[Figure: see text].

Artificial ionospheric layers during pump frequency stepping near the 4th gyroharmonic at HAARP

We report on artificial descending plasma layers created in the ionosphere F region by high-power high-frequency (HF) radio waves from High-frequency Active Auroral Research Program at frequencies f(0) near the fourth electron gyroharmonic 4f(ce). The data come from concurrent measurements of the secondary escaping radiation from the HF-pumped ionosphere, also known as stimulated electromagnetic emission, reflected probing signals at f(0), and plasma line radar echoes. The artificial layers appeared only for injections along the magnetic field and f(0)>4f(ce) at the nominal HF interaction altitude in the background ionosphere. Their average downward speed ~0.5 km/s holds until the terminal altitude where the local fourth gyroharmonic matches f(0). The total descent increases with the nominal offset f(0)-4f(ce).

Curative resection for low rectal adenocarcinoma: abdomino-perineal vs anterior resection

OBJECTIVE

Local recurrence after abdomino-perineal excision of the rectum for tumours has been reported to occur in up to a third of patients in contrast to 4% after restorative anterior resection.

METHOD

Low rectal tumours were defined as tumours within 8 cm of the anal verge and were treated by either stapled low anterior resection (SLAR) or abdomino-perineal excision of the rectum (APER). One hundred and seventy-eight patients with tumours in the lower third of the rectum (30% of 591 rectal cancers) underwent surgical resection between 1980 and 2001. Data were collected prospectively; 68 (38%) had SLAR and 110 (62%) had APER with median follow up of approximately 12 years; 54 SLAR (79%) and 76 APER (69%) had curative procedures on clinical and pathological criteria.

RESULTS

Local and distant recurrence occurred in seven (13%) and eight (15%) patients in the SLAR group and six (8%) and 14 (18%) patients in the APER group, respectively. Overall 5-year survival was 63% and 60% in the SLAR and APER groups, respectively

CONCLUSION

For rectal cancers within 8 cm of the anal verge, both procedures achieved equivalent results measured by low local recurrence rates and overall survival.

How can experiences of patients and carers influence the clinical care of large bowel cancer?

A qualitative project was designed to investigate the care of large bowel cancer from patients' and carers' perspectives using semi-structured interviews; tape-recorded, transcribed and analysed; to identify recurrent themes. Forty-nine patients treated surgically for bowel cancer from three hospital trusts in West Surrey were visited at home, and eight of their carers attended a focus group from a choice of three geographical locations. Five main themes identified: experience of symptoms; general practitioner (GP) management; impact of diagnosis; perceptions of clinical care and treatment; information needs. Results showed that patients and carers were ignorant of the symptoms and signs of large bowel cancer and wanted more information. They were satisfied when the GP took symptoms seriously and referred promptly. Three groups of patients were particularly vulnerable: those requiring stomas (25), those diagnosed with polyps initially (11) and patients admitted as an emergency (7). Specialist nurses were seen as the main source of written information and support, which was most needed at the time of diagnosis and discharge. The public needs more accessible information about the symptoms and signs of bowel cancer. Referral to multiprofessional bowel cancer teams is essential to provide appropriate support and clear information from the time of diagnosis throughout the care pathway. Recommended strategies for improving clinical care are outlined.

Effect of faecal occult blood testing on colorectal cancer mortality in the surveillance of subjects at moderate risk of colorectal neoplasia: a case-control study

Colonoscopy is the established method of surveillance of subjects at high risk of developing colorectal neoplasia. Its role in the surveillance of a population at moderate risk is less clear, however, as the procedure is expensive, time consuming and occasionally hazardous. The aim of this study was to estimate by case-control methods the effect of faecal occult blood (FOB) screening on colorectal cancer (CRC) mortality in a population at moderate risk of developing CRC. Screening by FOB testing prior to diagnosis in patients over the age of 45 years who died of CRC diagnosed in 1989-1998 was compared with screening in controls matched with the case for age and sex. Information about episodes of FOB testing and potential confounders was obtained from the data collection system of the screening programme. Cases were less likely than controls to have ever been screened, with an odds ratio of 0.64 (95% confidence interval 0.34-1.15) for exposure to at least one FOB testing. There was no significant difference between the sub-groups according to gender, age at diagnosis or location of the cancer. The inverse association between screening for faecal occult blood and fatal colorectal cancer suggests that screening in a population at moderate risk of CRC can reduce mortality from CRC in this group.

A 10-year prospective audit of outcome of surgical treatment for colorectal carcinoma

The outcome of 555 patients who underwent surgery under the care of a surgeon with an interest in colorectal disease was examined prospectively over a 10-year period with no exclusions. There was a 4.7 percent incidence of clinical leaks (10 percent for anterior resection) and an overall corrected 10-year survival rate after curative surgery of 58, 59 and 48 percent for right colonic, left colonic and rectal tumours respectively. The incidence of isolated local recurrence was 8 percent after curative surgery for carcinoma of the rectum. Twenty-five percent of patients with rectal tumours required abdominoperineal excision. Patients who underwent curative abdominoperineal excision of the rectum had corrected 5- and 10-year survival rates of 48 and 36 percent, compared with 60 and 58 percent respectively for curative anterior resection. The perioperative mortality rate of those undergoing palliative surgery was 8 percent, and 75 percent died within 2 years from distant and not local disease. A policy of always attempting resection was validated by the fact that 99 percent of primary tumours were removed with a low perioperative mortality rate (4 percent overall), a high curative resection rate and a low morbidity rate.

Informal out-patient discussions with patients following surgery for large bowel cancer: are they beneficial?

The value of informal out-patient discussions as a useful, additional method of assessment for both patient and doctor during a busy out-patient clinic is considered. One hundred patients were interviewed by a research or stoma care sister at their first follow-up visit after surgery for large bowel cancer in the combined Oncology/Surgical out-patient clinic of a district general hospital. Particular interest was taken of patients' awareness of diagnosis (85% understood) and operation (93% understood), general well-being (74% had resumed limited activity), dependency on the primary health care team (13%), family history of bowel or associated cancers (as many as 31% had one or more first degree relatives affected) and the suitability for research trials, including adjuvant radiotherapy/chemotherapy (29% were entered). Patients appreciated the opportunity to discuss problems at a particularly stressful period of their lives. It would seem that when problems are identified and an overall assessment of patients' needs made, relevant information is provided for doctors which is influential in improving patient care.

A screening clinic for relatives of patients with colorectal cancer in a district general hospital

A family cancer screening clinic was set up to screen and counsel subjects at above average risk of developing colorectal cancer. Criteria for referral were one first degree relative under 50 years or two of any age with colorectal cancer. Pedigree information was used to estimate lifetime risks of developing colorectal cancer and offer appropriate screening: colonoscopy for high risks (greater than 1 in 10), faecal occult blood testing for lower risks. One hundred and eleven subjects from 76 families were seen over four years. Forty two families gave a pedigree consistent with dominantly inherited non-polyposis colorectal cancer syndrome (HNPCC). Three subjects from one family were found to have familial adenomatous polyposis. Ninety two colonoscopies yielded 21 patients with polyps (12 had tubular adenomas, including one with early malignant invasion). Thirty three per cent (four of 12) of the tubular adenomas were beyond the reach of a flexible sigmoidoscope. Three hundred and forty two further high risk relatives were identified from the family history.

Vitamin A supplementation enhances specific IgG antibody levels and total lymphocyte numbers while improving morbidity in measles

The effect of vitamin A supplementation on selected factors of immunity was tested in African children (ages 4 to 24 months with complicated measles) during a randomized double-blind intervention trial. Placebo (n = 31) and treated groups (n = 29) had similar baseline characteristics. The supplemented group had significant reductions in morbidity (expressed as integrated morbidity scores) during the acute (Day 8, P = 0.006) and chronic (Day 42, P = 0.02; 6 months; P = 0.002) phases. In the treated group there was an increase in total number of lymphocytes (Day 42, P = 0.05) and measles IgG antibody concentrations (Day 8, P = 0.02), both of which have consistently been previously shown to correlate more closely with outcome in measles than other immunologic, clinical and radiologic factors. Interleukin 2 and plasma complement values were unaffected by vitamin A supplementation. These findings reinforce results from animal studies that show that the pathways of vitamin A activity in decreasing morbidity and mortality are partly founded on selective immunopotentiation.

Vitamin A supplementation reduces measles morbidity in young African children: a randomized, placebo-controlled, double-blind trial

The effects of vitamin A supplementation on measles morbidity are unclear. Sixty hospitalized children aged 4-24 mo with complicated measles received a World Health Organization--(WHO) recommended dose of vitamin A or placebo. The two groups were comparable in known covariants of measles severity: weight-for-age percentiles, overcrowding, rash, total lymphocytes, and serum concentrations of zinc, albumin, prealbumin, retinol-binding protein, and vitamins A and E. Ninety percent of the patients had hyporetinemia. Integrated morbidity scores, determined by severity of condition (eg, diarrhoea, herpes, and respiratory-tract infection) were assigned on day 8 and 6 wk and 6 mo; these were reduced by 82%, 61%, and 85%, respectively, in the supplemented group, which was mainly due to reduced respiratory-tract infection. There was one death in the placebo group. At 6 wk weight gain was significant in the supplemented group. Despite the selected sample, attention to multiple covariates enhances the validity of the data obtained and supports the current WHO recommendations for vitamin A supplementation during measles.