Separability Transitions in Topological States Induced by Local Decoherence.

We study states with intrinsic topological order subjected to local decoherence from the perspective of separability, i.e., whether a decohered mixed state can be expressed as an ensemble of short-range entangled pure states. We focus on toric codes and the X-cube fracton state and provide evidence for the existence of decoherence-induced separability transitions that precisely coincide with the threshold for the feasibility of active error correction. A key insight is that local decoherence acting on the "parent" cluster states of these models results in a Gibbs state. As an example, for the 2D (3D) toric code subjected to bit-flip errors, we show that the decohered density matrix can be written as a convex sum of short-range entangled states for p>p_{c}, where p_{c} is related to the paramagnetic-ferromagnetic transition in the 2D (3D) random bond Ising model along the Nishimori line.

Competing Nodal d-Wave Superconductivity and Antiferromagnetism.

Competing unconventional superconductivity and antiferromagnetism widely exist in several strongly correlated quantum materials whose direct simulation generally suffers from fermion sign problem. Here, we report unbiased quantum Monte Carlo (QMC) simulations on a sign-problem-free repulsive toy model with same on site symmetries as the standard Hubbard model on a 2D square lattice. Using QMC simulations, supplemented with mean-field and continuum field-theory arguments, we find that it hosts three distinct phases: a nodal d-wave phase, an antiferromagnet, and an intervening phase which hosts coexisting antiferromagnetism and nodeless d-wave superconductivity. The transition from the coexisting phase to the antiferromagnet is described by the 2+1-D XY universality class, while the one from the coexisting phase to the nodal d-wave phase is described by the Heisenberg-Gross-Neveu theory. The topology of our phase diagram resembles that of layered organic materials which host pressure tuned Mott transition from antiferromagnet to unconventional superconductor at half-filling.

Kondo Breakdown in a Spin-1/2 Chain of Adatoms on a Dirac Semimetal.

We consider a spin-1/2 Heisenberg chain coupled via a Kondo interaction to two-dimensional Dirac fermions. The Kondo interaction is irrelevant at the decoupled fixed point, leading to the existence of a Kondo-breakdown phase and a Kondo-breakdown critical point separating such a phase from a heavy Fermi liquid. We reach this conclusion on the basis of a renormalization group analysis, large-N calculations as well as extensive auxiliary-field quantum Monte Carlo simulations. We extract quantities such as the zero-bias tunneling conductance which will be relevant to future experiments involving adatoms on semimetals such as graphene.

Entanglement Renyi Negativity across a Finite Temperature Transition: A Monte Carlo Study.

Quantum entanglement is fragile to thermal fluctuations, which raises the question whether finite temperature phase transitions support long-range entanglement similar to their zero temperature counterparts. Here we use quantum Monte Carlo simulations to study the third Renyi negativity, a generalization of entanglement negativity, as a proxy of mixed-state entanglement in the 2D transverse field Ising model across its finite temperature phase transition. We find that the area-law coefficient of the Renyi negativity is singular across the transition, while its subleading constant is zero within the statistical error. This indicates that the entanglement is short-range at the critical point despite a divergent correlation length. Renyi negativity in several exactly solvable models also shows qualitative similarities to that in the 2D transverse field Ising model.

Detecting Topological Order at Finite Temperature Using Entanglement Negativity.

We propose a diagnostic for finite temperature topological order using "topological entanglement negativity," the long-range component of a mixed-state entanglement measure. As a demonstration, we study the toric code model in d spatial dimensions for d=2,3,4, and find that when topological order survives thermal fluctuations, it possesses a nonzero topological entanglement negativity, whose value is equal to the topological entanglement entropy at zero temperature. Furthermore, we show that the Gibbs state of 2D and 3D toric code at any nonzero temperature, and that of 4D toric code above a certain critical temperature, can be expressed as a convex combination of short-range entangled pure states, consistent with the absence of topological order.

Renyi entropy of chaotic eigenstates.

Using arguments built on ergodicity, we derive an analytical expression for the Renyi entanglement entropies which, we conjecture, applies to the finite-energy density eigenstates of chaotic many-body Hamiltonians. The expression is a universal function of the density of states and is valid even when the subsystem is a finite fraction of the total system-a regime in which the reduced density matrix is not thermal. We find that in the thermodynamic limit, only the von Neumann entropy density is independent of the subsystem to the total system ratio V_{A}/V, while the Renyi entropy densities depend nonlinearly on V_{A}/V. Surprisingly, Renyi entropies S_{n} for n>1 are convex functions of the subsystem size, with a volume law coefficient that depends on V_{A}/V, and exceeds that of a thermal mixed state at the same energy density. We provide two different arguments to support our results: the first one relies on a many-body version of Berry's formula for chaotic quantum-mechanical systems, and is closely related to the eigenstate thermalization hypothesis. The second argument relies on the assumption that for a fixed energy in a subsystem, all states in its complement allowed by the energy conservation are equally likely. We perform an exact diagonalization study on quantum spin-chain Hamiltonians to test our analytical predictions.

Indocyanine Green Angiography to Prognosticate Healing of Foot Ulcer in Critical Limb Ischemia: A Novel Technique.

BACKGROUND: To predict wound healing in patients with critical limb ischemia (CLI) is an ongoing issue. Current methods such as ankle-brachial index (ABI), color Doppler and transcutaneous oxygen pressure (TCPO2), and computed tomography angiography are lacking in demonstrating regional perfusion. Indocyanine green angiography (ICGA) has the potential to provide regional perfusion information lacking in other methods. This study was conducted to demonstrate successes of revascularization procedure in CLI patients based on ICGA data. METHODS: A total of 47 patients with grade 2 or grade 3 University of Texas Wound Classification System ischemic foot ulcer undergoing lower limb revascularization procedure were included in this study, from July 2014 to May 2016. ICGA with intravenous 0.1 mg/kg of 0.1% indocyanine green dye was performed before and after revascularization procedure. ICGA data maximum unit, blush time, and blush rate were compared between prerevascularization and postrevascularization data, along with ABI and TCPO2. RESULTS: Out of 47 patients (45 males and 2 females), 43 underwent endovascular revascularization and 4 underwent open procedure. Of all, 76.6% of patients were diabetic and 46.8% were hypertensive. Also, 31.9% had coronary artery disease, 21.2% had history of cerebrovascular disease, 23% had chronic kidney disease, and 74.4% were chronic smokers. A total of 37 patients' ulcer healed completely on follow-up with significant improvement (P < 0.05) in preoperative and postoperative ABI, TCPO2, and ICGA data. Ten patients' ulcer did not heal in the follow-up period. In those 10 patients, preoperative and postoperative ABI and TCPO2 improved, but ICGA data were not improved postoperatively (P > 0.05). CONCLUSIONS: ICGA is an evolving tool to quantify regional perfusion in CLI. ICGA parameters provide qualitative real-time visual images of perfusion in area of interest as well as quantitative information of perfusion.

Quantum Monte Carlo Simulation of Frustrated Kondo Lattice Models.

The absence of the negative sign problem in quantum Monte Carlo simulations of spin and fermion systems has different origins. World-line based algorithms for spins require positivity of matrix elements whereas auxiliary field approaches for fermions depend on symmetries such as particle-hole symmetry. For negative-sign-free spin and fermionic systems, we show that one can formulate a negative-sign-free auxiliary field quantum Monte Carlo algorithm that allows Kondo coupling of fermions with the spins. Using this general approach, we study a half-filled Kondo lattice model on the honeycomb lattice with geometric frustration. In addition to the conventional Kondo insulator and antiferromagnetically ordered phases, we find a partial Kondo screened state where spins are selectively screened so as to alleviate frustration, and the lattice rotation symmetry is broken nematically.

A Rare Entity: Traumatic Thoracic Aortic Injury in a Patient with Aberrant Right Subclavian Artery.

BACKGROUND: Aberrant right subclavian artery is an uncommon entity incidence ranging from 0.5 to 2.5%. Management of thoracic aortic injury in the presence of such anomalies can be a challenge. We present here a case of traumatic aortic injury, which was incidentally found to have an asymptomatic aberrant right subclavian artery. The patient was managed by an endovascular repair of thoracic aortic injury with an endograft and a right carotid to subclavian artery bypass as a hybrid procedure. METHODS: A 40-year male patient was brought to the emergency in shock with an alleged history of road traffic accident an hour back. After initial resuscitation as per advance trauma life support protocol, imaging revealed thoracic aortic injury with aberrant right subclavian artery with multiple rib and bilateral humerus fracture. After primary stabilization of arm fractures, the patient was shifted to a hybrid operation room. As the aortic injury was within 10 mm of the origin of both subclavian arteries, it was decided to cover the origin of both subclavian arteries and land the endograft distal to the left carotid artery origin. Since there was a right dominant vertebral artery on imaging, right carotid to right subclavian artery bypass was done with expanded polytetrafluoroethylene graft to prevent posterior circulatory stroke along with thoracic endovascular aortic repair to seal the thoracic aortic injury. RESULTS: After endovascular repair of thoracic aortic injury, left subclavian artery perfusion was maintained through left vertebral artery; and hence, revascularization of left subclavian artery was deferred. After management of all fractures, the patient was discharged 3 weeks after the date of admission without any complications. At 6 months follow-up, patient was stable and images showed patent bypass graft and sealed aortic injury. CONCLUSIONS: In a trauma setting with multiple injuries, hybrid procedure with a thoracic endograft is associated with low mortality and morbidity; hence, it is the treatment of choice for thoracic aortic injury over open surgical repair. A hybrid suite can be life and time saving in situations which mandate simultaneous endovascular repair along with surgical revascularization when indicated, especially in cases with aberrant aortic arch anatomy.

All Majorana Models with Translation Symmetry are Supersymmetric.

We establish results similar to Kramers and Lieb-Schultz-Mattis theorems but involving only translation symmetry and for Majorana modes. In particular, we show that all states are at least doubly degenerate in any one- and two-dimensional array of Majorana modes with translation symmetry, periodic boundary conditions, and an odd number of modes per unit cell. Moreover, we show that all such systems have an underlying N=2 supersymmetry and explicitly construct the generator of the supersymmetry. Furthermore, we establish that there cannot be a unique gapped ground state in such one-dimensional systems with antiperiodic boundary conditions. These general results are fundamentally a consequence of the fact that translations for Majorana modes are represented projectively, which in turn stems from the anomalous nature of a single Majorana mode. An experimental signature of the degeneracy arising from supersymmetry is a zero-bias peak in tunneling conductance.

Double Barrel In Situ Recanalization of Thrombosed Nonretrievable IVC filter.

We report a case of endovascular recanalization of complete thrombotic occlusion of the inferior vena cava (IVC) and bilateral iliac veins using the architectural knowledge of the in situ permanent IVC filter in a 23-year-old male. The infrarenal permanent IVC filter was TRAPEASE permanent vena cava filter (Cordis) placed at an outstation hospital for pulmonary embolism. Being permanent variant of filter, percutaneous removal was not possible. The patient had severe venous claudication and an attempt to recanalize the blocked filter was considered, in view of the age no justifiable indication for a long-term filter. After pharmacomechanical catheter-directed thrombolysis, there was residual focal flow-limiting thrombus within the filter. The design of the Trapease Cordis filter was instrumental in our decision to attempt to recanalize the filter in situ using 2 parallel stents with the filter struts as anchoring pillars in a double-barrel alignment. In similar cases of persistent Trapease filter-related thrombotic occlusion of the IVC, this double barrel in situ recanalization shall be a viable alternative to the well-described technique of crushing the filter and recanalizing it with a single stent.

Entanglement monotonicity and the stability of gauge theories in three spacetime dimensions.

We employ the recent results on the generalization of the central charge theorem to three spacetime dimensions to derive nonperturbative results for several strongly interacting quantum field theories, including quantum electrodynamics (QED-3), and the theory corresponding to certain quantum phase transitions in condensed matter systems. In particular, by demanding that the universal constant part of the entanglement entropy decreases along the renormalization group flow (F theorem), we find sufficient conditions for the stability of QED-3 against chiral symmetry breaking and confinement. Using similar ideas, we derive strong constraints on the nature of quantum critical points in condensed matter systems with topological order.

Emergent space-time supersymmetry at the boundary of a topological phase.

In contrast to ordinary symmetries, supersymmetry (SUSY) interchanges bosons and fermions. Originally proposed as a symmetry of our universe, it still awaits experimental verification. Here, we theoretically show that SUSY emerges naturally in condensed matter systems known as topological superconductors. We argue that the quantum phase transitions at the boundary of topological superconductors in both two and three dimensions display SUSY when probed at long distances and times. Experimental consequences include exact relations between quantities measured in disparate experiments and, in some cases, exact knowledge of the universal critical exponents. The topological surface states themselves may be interpreted as arising from spontaneously broken SUSY, indicating a deep relation between topological phases and SUSY.

Entanglement of interacting fermions in quantum Monte Carlo calculations.

Given a specific interacting quantum Hamiltonian in a general spatial dimension, can one access its entanglement properties, such as the entanglement entropy corresponding to the ground state wave function? Even though progress has been made in addressing this question for interacting bosons and quantum spins, as yet there exist no corresponding methods for interacting fermions. Here we show that the entanglement structure of interacting fermionic Hamiltonians has a particularly simple form-the interacting reduced density matrix can be written as a sum of operators that describe free fermions. This decomposition allows one to calculate the Renyi entropies for Hamiltonians which can be simulated via determinantal quantum Monte Carlo calculations, while employing the efficient techniques hitherto available only for free fermions. The method presented works for the ground state, as well as for the thermally averaged reduced density matrix.

Entanglement entropy of critical spin liquids.

Quantum spin liquids are phases of matter whose internal structure is not captured by a local order parameter. Particularly intriguing are critical spin liquids, where strongly interacting excitations control low energy properties. Here we calculate their bipartite entanglement entropy that characterizes their quantum structure. In particular we calculate the Renyi entropy S(2) on model wave functions obtained by Gutzwiller projection of a Fermi sea. Although the wave functions are not sign positive, S(2) can be calculated on relatively large systems (>324 spins) using the variational Monte Carlo technique. On the triangular lattice we find that entanglement entropy of the projected Fermi sea state violates the boundary law, with S(2) enhanced by a logarithmic factor. This is an unusual result for a bosonic wave function reflecting the presence of emergent fermions. These techniques can be extended to study a wide class of other phases.

Non-Abelian spin liquid in a spin-one quantum magnet.

We study a time-reversal invariant non-Abelian spin-liquid state in an SU(2) symmetric spin S=1 quantum magnet on a triangular lattice. The spin liquid is obtained by quantum disordering a noncollinear nematic state. We show that such a spin liquid cannot be obtained by the standard projective construction for spin liquids. We also study the phase transition between the spin liquid and the noncollinear nematic state and show that it cannot be described within the Landau-Ginzburg-Wilson paradigm.

Endovascular treatment for peripheral pulmonary artery aneurysm.

A 42-year-old male presented with recurrent hemoptysis owing to a leaking peripheral pulmonary artery aneurysm. He was treated with selective coil embolization of the right posterior basal segmental artery to achieve hemostasis. This case is reported for its unsuspected presentation and rarity and to highlight the use of catheter coil embolization to achieve endovascular exclusion of the aneurysm from pulmonary circulation.

Topological spin Hall states, charged skyrmions, and superconductivity in two dimensions.

We study the properties of two dimensional topological spin Hall insulators which arise through spontaneous breakdown of spin symmetry in systems that are spin rotation invariant. Such a phase breaks spin rotation but not time reversal symmetry and has a vector order parameter. Skyrmion configurations in this vector order parameter are shown to have an electric charge that is twice the electron charge. When the spin Hall order is destroyed by condensation of Skyrmions superconductivity results. This may happen either through doping or at fixed filling by tuning interactions to close the Skyrmion gap. In the latter case the superconductor-spin Hall insulator quantum phase transition can be second order even though the two phases break distinct symmetries.

Quantum spin nematics, dimerization, and deconfined criticality in quasi-1D spin-one magnets.

We study theoretically the destruction of spin nematic order due to quantum fluctuations in quasi-one-dimensional spin-1 magnets. If the nematic ordering is disordered by condensing disclinations, then quantum Berry phase effects induce dimerization in the resulting paramagnet. We develop a theory for a Landau-forbidden second order transition between the spin nematic and dimerized states found in recent numerical calculations. Numerical tests of the theory are suggested.