[Autologous reconstructive surgery and intestinal rehabilitation in the management of short bowel syndrome]. / A rövidbél-szindróma korszeru sebészi kezelése: autológ rekonstrukció és intestinalis rehabilitáció.

Based on the latest definition, short bowel syndrome is defined as intestinal failure due to the loss of significant small bowel length or function, when the homeostasis and growth can only be maintained with intravenous supplementation of fluid, electrolytes and macronutrients. The natural adaptation of the short bowel can only compensate for the loss up to a certain level. According to this, we differentiate (1) acute, (2) prolonged and (3) chronic types of intestinal failure/short bowel syndrome. The most common causes are necrotising enterocolits, intestinal malrotation and volvulus, gastroschisis and ileal atresia. The management of type 3 short bowel syndrome has evolved significantly during the last decades, due to the multidisciplinary approach, hence the survival and quality of life of the patients have improved and transplantation is rarely necessary. Our aim was to review the most important considerations of intestinal rehabilitation, like management of increased gastrin secretion, high output stoma, decreased transit time, central venous lines, enteral and parenteral nutrition and the enhancement of the natural adaptation. We reviewed the former and the latest options of the autologous intestinal reconstructive surgery (AIRS) like the reversed segment, small bowel interposition, ileocaecal valve replacement, bowel lengthening and tailoring (LILT, STEP and SILT), controlled bowel expansion and the latest results with distraction enterogenesis and tissue engineering. Orv Hetil. 2020; 161(7): 243-251.

Continuum Limits of Homogeneous Binary Trees and the Thompson Group.

Tree tensor network descriptions of critical quantum spin chains are empirically known to reproduce correlation functions matching conformal field theory (CFT) predictions in the continuum limit. It is natural to seek a more complete correspondence, additionally incorporating dynamics. On the CFT side, this is determined by a representation of the diffeomorphism group of the circle. In a remarkable series of papers, Jones outlined a research program where the Thompson group T takes the role of the latter in the discrete setting, and representations of T are constructed from certain elements of a subfactor planar algebra. He also showed that, for a particular example of such a construction, this approach only yields-in the continuum limit-a representation which is highly discontinuous and hence unphysical. Here we show that the same issue arises generically when considering tree tensor networks: the set of coarse-graining maps yielding discontinuous representations has full measure in the set of all isometries. This extends Jones's no-go example to typical elements of the so-called tensor planar algebra. We also identify an easily verified necessary condition for a continuous limit to exist. This singles out a particular class of tree tensor networks. Our considerations apply to recent approaches for introducing dynamics in holographic codes.

Universal Uhrig Dynamical Decoupling for Bosonic Systems.

We construct efficient deterministic dynamical decoupling schemes protecting continuous-variable degrees of freedom. Our schemes target decoherence induced by quadratic system-bath interactions with analytic time dependence. We show how to suppress such interactions to Nth order using only N pulses. Furthermore, we show how to homogenize a 2^{m}-mode bosonic system using only (N+1)^{2m+1} pulses, yielding-up to the Nth order-an effective evolution described by noninteracting harmonic oscillators with identical frequencies. The decoupled and homogenized system provides natural decoherence-free subspaces for encoding quantum information. Our schemes only require pulses which are tensor products of single-mode passive Gaussian unitaries and swap gates between pairs of modes.

Quantum advantage with shallow circuits.

Quantum effects can enhance information-processing capabilities and speed up the solution of certain computational problems. Whether a quantum advantage can be rigorously proven in some setting or demonstrated experimentally using near-term devices is the subject of active debate. We show that parallel quantum algorithms running in a constant time period are strictly more powerful than their classical counterparts; they are provably better at solving certain linear algebra problems associated with binary quadratic forms. Our work gives an unconditional proof of a computational quantum advantage and simultaneously pinpoints its origin: It is a consequence of quantum nonlocality. The proposed quantum algorithm is a suitable candidate for near-future experimental realizations, as it requires only constant-depth quantum circuits with nearest-neighbor gates on a two-dimensional grid of qubits (quantum bits).

Matrix Product Approximations to Multipoint Functions in Two-Dimensional Conformal Field Theory.

Matrix product states (MPSs) illustrate the suitability of tensor networks for the description of interacting many-body systems: ground states of gapped 1D systems are approximable by MPSs, as shown by Hastings [M. B. Hastings, J. Stat. Mech. (2007) P08024]. By contrast, whether MPSs and more general tensor networks can accurately reproduce correlations in critical quantum systems or quantum field theories has not been established rigorously. Ample evidence exists: entropic considerations provide restrictions on the form of suitable ansatz states, and numerical studies show that certain tensor networks can indeed approximate the associated correlation functions. Here, we provide a complete positive answer to this question in the case of MPSs and 2D conformal field theory: we give quantitative estimates for the approximation error when approximating correlation functions by MPSs. Our work is constructive and yields an explicit MPS, thus providing both suitable initial values and a rigorous justification of variational methods.

Classification of topologically protected gates for local stabilizer codes.

Given a quantum error correcting code, an important task is to find encoded operations that can be implemented efficiently and fault tolerantly. In this Letter we focus on topological stabilizer codes and encoded unitary gates that can be implemented by a constant-depth quantum circuit. Such gates have a certain degree of protection since propagation of errors in a constant-depth circuit is limited by a constant size light cone. For the 2D geometry we show that constant-depth circuits can only implement a finite group of encoded gates known as the Clifford group. This implies that topological protection must be "turned off" for at least some steps in the computation in order to achieve universality. For the 3D geometry we show that an encoded gate U is implementable by a constant-depth circuit only if UPU(†) is in the Clifford group for any Pauli operator P. This class of gates includes some non-Clifford gates such as the π/8 rotation. Our classification applies to any stabilizer code with geometrically local stabilizers and sufficiently large code distance.

Classical capacity of quantum thermal noise channels to within 1.45 bits.

We find a tight upper bound for the classical capacity of quantum thermal noise channels that is within 1/ln2 bits of Holevo's lower bound. This lower bound is achievable using unentangled, classical signal states, namely, displaced coherent states. Thus, we find that while quantum tricks might offer benefits, when it comes to classical communication, they can only help a bit.

A strong converse for classical channel coding using entangled inputs.

A fully general strong converse for channel coding states that when the rate of sending classical information exceeds the capacity of a quantum channel, the probability of correctly decoding goes to zero exponentially in the number of channel uses, even when we allow code states which are entangled across several uses of the channel. Such a statement was previously only known for classical channels and the quantum identity channel. By relating the problem to the additivity of minimum output entropies, we show that a strong converse holds for a large class of channels, including all unital qubit channels, the d-dimensional depolarizing channel and the Werner-Holevo channel. This further justifies the interpretation of the classical capacity as a sharp threshold for information transmission.

Postselection technique for quantum channels with applications to quantum cryptography.

We propose a general method for studying properties of quantum channels acting on an n-partite system, whose action is invariant under permutations of the subsystems. Our main result is that, in order to prove that a certain property holds for an arbitrary input, it is sufficient to consider the case where the input is a particular de Finetti-type state, i.e., a state which consists of n identical and independent copies of an (unknown) state on a single subsystem. Our technique can be applied to the analysis of information-theoretic problems. For example, in quantum cryptography, we get a simple proof for the fact that security of a discrete-variable quantum key distribution protocol against collective attacks implies security of the protocol against the most general attacks. The resulting security bounds are tighter than previously known bounds obtained with help of the exponential de Finetti theorem.

Small accessible quantum information does not imply security.

The security of quantum key distribution is typically defined in terms of the mutual information between the distributed key S and the outcome of an optimal measurement applied to the adversary's system. We show that even if this so-called accessible information is small, the key S might not be secure enough to be used in applications such as one-time pad encryption. This flaw is due to a locking property of the accessible information: one additional (physical) bit of information can increase the accessible information by more than one bit.