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We develop the deformation theory of cohomological field theories (in short, CohFTs), which is done as a special case of a general deformation theory of morphisms of modular operads. This leads us to introduce two new natural extensions of the notion of a CohFT: homotopy (necessary algebraic toolkit to develop chain-level Gromov–Witten invariants) and quantum (with examples found in the works of Buryak and Rossi on integrable systems). The universal group of symmetries of morphisms of modular operads, based on Kontsevich's graph complex, is shown to be trivial. Using the tautological rings on moduli spaces of curves, we introduce a natural enrichment of Kontsevich's graph complex. This leads to universal groups of non-trivial symmetries of both homotopy and quantum CohFTs, which, in the latter case, is shown to contain both the prounipotent Grothendieck–Teichmüller group and the Givental group. [ABSTRACT FROM AUTHOR]

We show that the celebrated operad of pre-Lie algebras is very rigid: it has no "non-obvious" degrees of freedom from either of the three points of view: deformations of maps to and from the "three graces of operad theory", homotopy automorphisms, and operadic twisting. Examining the latter, it is possible to answer two questions of Markl from 2005 [Czechoslovak Math. J. 57 (2007), pp. 253–268; J. Lie Theory 17 (2007), pp. 241–261], including a Lie-theoretic version of the Deligne conjecture. [ABSTRACT FROM AUTHOR]

We give explicit combinatorial descriptions of three Schur functors arising in the theory of pre-Lie algebras. The first of them leads to a functorial description of the underlying vector space of the universal enveloping pre-Lie algebra of a given Lie algebra, strengthening the Poincaré-Birkhoff-Witt (PBW) theorem of Segal. The two other Schur functors provide functorial descriptions of the underlying vector spaces of the universal multiplicative enveloping algebra and of the module of Kähler differentials of a given pre-Lie algebra. An important consequence of such descriptions is an interpretation of the cohomology of a pre-Lie algebra with coefficients in a module as a derived functor for the category of modules over the universal multiplicative enveloping algebra. [ABSTRACT FROM AUTHOR]

We propose an algebraic viewpoint of the problem of deformation quantization of the so-called almost Poisson algebras, which are algebras with a commutative associative product and an antisymmetric bracket which is a biderivation but does not necessarily satisfy the Jacobi identity. From that viewpoint, the main result of the paper asserts that, by contrast with Poisson algebras, the only reasonable category of algebras in which almost Poisson algebras can be quantized is isomorphic to the category of almost Poisson algebras itself, and the trivial two-term quantization formula already gives a solution to the quantization problem. [ABSTRACT FROM AUTHOR]

To the memory of V. A. Artamonov (1946–2021) All algebras of a certain type are said to form a Nielsen–Schreier variety if every subalgebra of a free algebra is free. This property has been perceived as extremely rare; in particular, only six Nielsen–Schreier varieties of algebras with one binary operation have been discovered in prior work on this topic. We propose an effective combinatorial criterion for the Nielsen–Schreier property in the case of algebras over a field of zero characteristic; in our approach, operads play a crucial role. Using this criterion, we show that the well-known varieties of all pre-Lie algebras and of all Lie-admissible algebras are Nielsen–Schreier, and, quite surprisingly, that there are already infinitely many non-equivalent Nielsen–Schreier varieties of algebras with one binary operation and identities of degree four. [ABSTRACT FROM AUTHOR]

In the classical Batalin–Vilkovisky formalism, the BV operator Δ is a differential operator of order two with respect to the commutative product. In the differential graded setting, it is known that if the BV operator is homotopically trivial, then there is a tree level cohomological field theory induced on the homology; this is a manifestation of the fact that the homotopy quotient of the operad of BV algebras by Δ is represented by the operad of hypercommutative algebras. In this paper, we study generalized Batalin–Vilkovisky algebras where the operator Δ is of the given finite order. In that case, we unravel a new interesting algebraic structure on the homology whenever Δ is homotopically trivial. We also suggest that the sequence of algebraic structures arising in the higher order formalism is a part of a "trinity" of remarkable mathematical objects, fitting the philosophy proposed by Arnold in the 1990s. [ABSTRACT FROM AUTHOR]

We show that a finite dimensional monomial algebra satisfies the finite generation conditions of Snashall–Solberg for Hochschild cohomology if and only if it is Gorenstein. This gives, in the case of monomial algebras, the converse to a theorem of Erdmann–Holloway–Snashall–Solberg–Taillefer. We also give a necessary and sufficient combinatorial criterion for finite generation. [ABSTRACT FROM AUTHOR]

We propose a new method for computing motivic Donaldson–Thomas invariants of a symmetric quiver which relies on Koszul duality between supercommutative algebras and Lie superalgebras and completely bypasses cohomological Hall algebras. Specifically, we define, for a given symmetric quiver Q, a supercommutative quadratic algebra A Q , and study the Lie superalgebra g Q that corresponds to A Q under Koszul duality. We introduce an action of the first Weyl algebra on g Q and prove that the motivic Donaldson–Thomas invariants of Q may be computed via the Poincaré series of the kernel of the operator ∂ t . This gives a new proof of positivity for motivic Donaldson–Thomas invariants. Along the way, we prove that the algebra A Q is numerically Koszul for every symmetric quiver Q and conjecture that it is in fact Koszul; we show that this conjecture holds for a certain class of quivers. [ABSTRACT FROM AUTHOR]

We show that the integer cohomology rings of the moduli spaces of stable rational marked curves are Koszul. This answers an open question of Manin. Using the machinery of Koszul spaces developed by Berglund, we compute the rational homotopy Lie algebras of those spaces, and obtain some estimates for Betti numbers of their free loop spaces in case of torsion coefficients. We also prove and conjecture some generalisations of our main result. [ABSTRACT FROM AUTHOR]

Using methods of computer algebra, especially, Gröbner bases for submodules of free modules over polynomial rings, we solve a classification problem in theory of algebraic operads: we show that the only nontrivial (possibly inhomogeneous) distributive law between the operad of Lie algebras and the operad of commutative associative algebras is given by the Livernet–Loday formula deforming the Poisson operad into the associative operad. [ABSTRACT FROM AUTHOR]

We use Giraudo's construction of combinatorial operads from monoids to offer a conceptual explanation of the origins of Hoffbeck's path sequences of shuffle trees, and use it to define new monomial orders of shuffle trees. One such order is utilised to exhibit a quadratic Gröbner basis of the Poisson operad. [ABSTRACT FROM AUTHOR]

We construct for a forgetful functor from nonsymmetric operads to weight graded associative algebras, two functorial "enveloping operads," the right inverse and the left adjoint of the forgetful functor. Those functors turn out to be related by operadic Koszul duality, and that relationship can be utilized to exhibit an example of a binary quadratic non-Koszul operad for which the Ginzburg–Kapranov functional equation holds and an example of a binary quadratic Koszul operad for which the Koszul property cannot be established using Gröbner bases. Both examples resolve standing open problems in operad theory. We also apply the enveloping operad functors to get a new proof of the Lagrange inversion formula using homotopical algebra. [ABSTRACT FROM AUTHOR]

We introduce and study several new topological operads that should be regarded as nonsymmetric analogues of the operads of little 2‐discs, framed little 2‐discs, and Deligne–Mumford compactifications of moduli spaces of genus zero curves with marked points. These operads exhibit all the remarkable algebraic and geometric features that their classical analogues possess; in particular, it is possible to define a noncommutative analogue of the notion of cohomological field theory with similar Givental‐type symmetries. This relies on rich geometry of the analogues of the Deligne–Mumford spaces, coming from the fact that they admit several equivalent interpretations: as the toric varieties of Loday's realisations of the associahedra, as the brick manifolds recently defined by Escobar, and as the De Concini–Procesi wonderful models for certain subspace arrangements. [ABSTRACT FROM AUTHOR]

Future development of superconductor digital and mixed-signal ICs requires extensive testing with a large number of input/output (I/O) lines for applying independent bias controls, injecting test signals, and monitoring outputs of different sub-circuits. There is a growing need for a standardized test apparatus for a variety of complex superconducting chips and multichip modules (MCMs). Such a test apparatus must support many I/O lines, be easy and cost-effective to operate, and support prolonged automated testing. Existing test apparatus include liquid He cryoprobes and cryocooled custom digital-RF systems, both of which have drawbacks. Liquid He cryoprobes with universal wiring, such as 40 or 80 coaxial cables, are convenient to use. Cooled by immersion in a tank filled with liquid He, these cryoprobes allow rapid cool-down and warm-up. However, large consumption of liquid He, the cost of which has been steadily increasing worldwide, makes this solution rather expensive and wasteful. On the other hand, one can exploit the modular reconfigurability of HYPRES’ digital-RF receiver product to create a testbed for different ICs. Such a system uses the smallest commercially available closed-cycle refrigerator (∼1.2 kW) and has negligible operating cost. However, reconfiguration takes time and expertise since these products are specially designed with customized chip package and wiring to minimize the thermal load on the cryocooler. These low-maintenance systems are ideal for prolonged operation of a single chip, which is invaluable for superconductor electronics system developers and end-users. The integrated cryoelectronics testbed (ICE-T) combines the advantages of the liquid He cryoprobe and the cryocooled digital-RF product. By using a more powerful, commercially available, electrically powered closed-cycle refrigerator (7 kW), ICE-T alleviates the thermal constraints on wiring while maintaining very low operating cost. By separating the electrical and thermal subsystems, it maintains modularity without sacrificing the universality of the cryoprobe. A set of universal and custom electrical modules can be independently built and inserted in ICE-T. Universal inserts with 40 and 80 coaxial cables accommodate all chips with standard I/O pads like the familiar liquid He cryoprobes. Custom inserts for different classes of chips and MCMs are designed and built according to user requirements and specifications. The utility of the ICE-T was successfully demonstrated by testing a benchmark superconducting digital circuit at low frequency and an analog-to-digital converter chip clocked above 20 GHz. [ABSTRACT FROM PUBLISHER]

For a Koszul operad $\mathcal {P}$ , there are several existing approaches to the notion of a homotopy between homotopy morphisms of homotopy $\mathcal {P}$ -algebras. Some of those approaches are known to give rise to the same notions. We exhibit the missing links between those notions, thus putting them all into the same framework. The main nontrivial ingredient in establishing this relationship is the homotopy transfer theorem for homotopy cooperads due to Drummond-Cole and Vallette. [ABSTRACT FROM AUTHOR]

The article discusses the annual meeting of the professional organization Irish Mathematical Society (IMS) at Trinity College Dublin in Ireland on April 15-16, 2016 which featured talks on graph inequalities, universal approximation in analysis, and rigid symmetric frameworks.

By using the Coulomb gas technics we calculate the four-spin correlation function in the percolation q → 1 limit of the Potts model. It is known that the four-point functions define the actual fusion rules of a particular model. In this respect, we find that fusion of two spins, of dimension Δ σ = 5 96 , produce a new channel, in the 4-point function, which is due to the operator with dimension Δ = 5 / 8 . [ABSTRACT FROM AUTHOR]

It is shown that the general 3-point function 〈 Φ c Φ b Φ a 〉 , with continuous values of charges a , b , c of a statistical model operators, and the 3-point function of the Liouville model, could all be obtained by successive analytical continuations starting from the 3-point function of the minimal model. [ABSTRACT FROM AUTHOR]

We endow the de Rham cohomology of any Poisson or Jacobi manifold with a natural homotopy Frobenius manifold structure. This result relies on a minimal model theorem for multicomplexes and a new kind of a Hodge degeneration condition. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we initiate the study of the Givental group action on Cohomological Field Theories in terms of homotopical algebra. More precisely, we show that the stabilisers of Topological Field Theories in genus 0 (respectively in genera 0 and 1) are in one-to-one correspondence with commutative homotopy Batalin–Vilkovisky algebras (respectively wheeled commutative homotopy BV-algebras). [Copyright &y& Elsevier]

Abstract: In this paper, which is the second one in a series of two papers, we shall present two more solutions, non-minimal ones, for the parafermionic chiral algebra with , , being the principal parafermionic fields. [Copyright &y& Elsevier]

Abstract: We analyze, and prove, the associativity of the new parafermionic chiral algebra which has been announced some time ago, with principal parafermionic fields having the conformal dimension . In doing so we have developed a new method for analyzing the associativity of a given chiral algebra of parafermionic type, the method which might be of a more general significance than a particular conformal field theory studied in detail in this paper. Still, even in the context of our particular chiral algebra, of parafermions with , the new method allowed us to give a proof of associativity which we consider to be complete. [Copyright &y& Elsevier]

A custom-designed laboratory prototype of a four-stage Stirling-type pulse tube cryocooler was recently developed by Lockheed Martin for niobium integrated circuits (ICs) operating close to 4 K. Basic system performance has been verified by integration with a Nb IC test chip, with cells that include a high-speed rapid single flux quantum (RSFQ) binary counter. For 650 W total compressor power, extended stable operation of the counter at T = 4.5 K was demonstrated with a clock frequency up to 46 GHz, with 25 mW of excess cooling capacity on the coldest stage. The thermodynamic, electromagnetic, and mechanical performance are promising for the development of an improved compact cryocooler for practical superconducting electronic applications in fields such as wireless communications. [ABSTRACT FROM AUTHOR]

Abstract: Using the renormalization group approach, the Coulomb gas and the coset techniques, the effect of slightly relevant perturbations is studied for the second parafermionic field theory with the symmetry , for N odd. New fixed points are found and classified. [Copyright &y& Elsevier]

We report experimental results for chip-to-chip data communications on a superconducting Multi-Chip-Module (MCM) using a novel fabrication technique. The MCM was produced using a non-conductive adhesive to bond a 5-mm x 5-mm test chip to a 1-cm x 1-cm carrier. To our knowledge, this is the first time this technique was used for MCM assembly at cryogenic temperatures. The module demonstrated superior mechanical stability and protection from its environment during thermal cycling. The MCM also retained its electrical properties after multiple thermal cycling from room temperature to 4 K. We designed test circuits including various digital test benches, as well as analog test structures for bump characteristics. The superconducting circuitry successfully passed single-flux quanta at rates exceeding 50 Gbps. We measured error rates lower than 5 x 10-14 at 36Gbps using 100-micrometer-diameter In-Sn solder bumps, and lower than 6 x 10-14 at 57Gbps using 30-micrometer-diameter solder bumps. [ABSTRACT FROM AUTHOR]

Abstract: Using the renormalization group approach, the Coulomb gas and the coset techniques, the effect of slightly relevant perturbations is studied for the second parafermionic field theory with the symmetry . New fixed points are found and classified. [Copyright &y& Elsevier]

Abstract: We have constructed the parafermionic chiral algebra with the principal parafermionic fields having the conformal dimension and realizing the symmetry . [Copyright &y& Elsevier]

We construct two-dimensional conformal field theories with a ZN symmetry, based on the second solution of Fateev–Zamolodchikov for the parafermionic chiral algebra. Primary operators are classified according to their transformation properties under the dihedral group (ZN×Z2, where Z2 stands for the ZN charge conjugation), as singlets, ⌊(N−1)/2⌋ different doublets, and a disorder operator. In an assumed Coulomb gas scenario, the corresponding vertex operators are accommodated by the Kac table based on the weight lattice of the Lie algebra B(N−1)/2 when N is odd, and DN/2 when N is even. The unitary theories are representations of the coset SOn(N)×SO2(N)/SOn+2(N), with n=1,2,… . We suggest that physically they realize the series of multicritical points in statistical systems having a ZN symmetry. [Copyright &y& Elsevier]

Following our previous papers [Nucl. Phys. B 656 (2003) 259, Nucl. Phys. B 664 (2003) 477] we complete the construction of the parafermionic theory with the symmetry ZN based on the second solution of Fateev–Zamolodchikov for the corresponding parafermionic chiral algebra. In the present paper we construct the ZN parafermionic theory for N even. Primary operators are classified according to their transformation properties under the dihedral group (ZN×Z2, where Z2 stands for the ZN charge conjugation), as two singlets, doublet 1,2,…,N/2−1, and a disorder operator. In an assumed Coulomb gas scenario, the corresponding vertex operators are accommodated by the Kac table based on the weight lattice of the Lie algebra DN/2. The unitary theories are representations of the coset SOn(N)×SO2(N)/SOn+2(N), with n=1,2,…. We suggest that physically they realise the series of multicritical points in statistical systems having a ZN symmetry. [Copyright &y& Elsevier]

We construct a parafermionic conformal theory with the symmetry ZN, for N odd, based on the second solution of Fateev–Zamolodchikov for the corresponding parafermionic chiral algebra. Primary operators are classified according to their transformation properties under the dihedral group DN, as singlet, doublet 1,2,…,N−1/2, and disorder operators. In an assumed Coulomb gas scenario, the corresponding vertex operators are accommodated by the weight lattice of the Lie algebra B(N−1)/2. The unitary theories are representations of the coset SOn(N)×SO2(N)/SOn+2(N), with n=1,2,… . Physically, they realise the series of multicritical points in statistical theories having a DN symmetry. [Copyright &y& Elsevier]

A parafermionic conformal theory with the symmetry Z5 is constructed, based on the second solution of Fateev–Zamolodchikov for the corresponding parafermionic chiral algebra.The primary operators of the theory, which are the singlet, doublet 1, doublet 2, and disorder operators, are found to be accommodated by the weight lattice of the classical Lie algebra B2. The finite Kac tables for unitary theories are defined and the formula for the conformal dimensions of primary operators is given. [Copyright &y& Elsevier]

We study systems of M Potts models coupled by their local energy density. Each model is taken to have a distinct number of states, and the permutational symmetry SM present in the case of identical coupled models is thus broken initially. The duality transformations within the space of 2M−1 multi-energy couplings are shown to have a particularly simple form. The selfdual manifold has dimension DM=2M−1−1. Specialising to the case M=3, we identify a unique non-trivial critical point in the three-dimensional selfdual space. We compare its critical exponents as computed from the perturbative renormalisation group with numerical transfer matrix results. Our main objective is to provide evidence that at the critical point of three different coupled models the symmetry S3 is restored. [Copyright &y& Elsevier]

Powder samples of Cr3+-doped δ*-Al 2 O 3 with particles sizes of 10–70 nm were obtained by combustion method. It is shown for the first time that Cr3+ ions in the δ*-Al 2 O 3 occupy octahedral sites in the bulk and at the surface of the nanosized particles. The photoluminescence spectra of Cr3+ in δ*-Al 2 O 3 consist of several relatively narrow lines (R-lines luminescence) in the 680–720 nm range, which are due to the 2E g → 4A 2g transitions. The local structure around Cr3+ ions inside the nanoparticles is shown to differ from that of Cr3+ located in the surface layer, which results in essential differences in the full width at half maximum values (14 cm−1 vs. 39 cm−1 at 77 K) and in red shift of the R-lines with increasing temperature from 77 to 293 K (20 cm−1 vs. ~11 cm−1). It was found that the Cr3+-doped δ*-Al 2 O 3 exhibits some striking features, including an unexpectedly high crystal-field strength at the interior Cr3+ site and an unusually high concentration of surface Cr3+ centers. Possible reasons for these features are discussed. The results obtained are anticipated to be useful for the monitoring of processes involved in the preparation of ceramics and composites based on Al 2 O 3 :Cr3+. [Display omitted] • The luminescent properties of Сr3+ in nanosized δ*-Al 2 O 3 are analyzed. • Two types of Сr3+ related centers (regular and surface) are observed. • In the 77–293 K range, all the Cr3+centers show emissions of the 2E g.→4A 2g type. • Structural disorder degree as a notable characteristic of Al 2 O 3 polymorphs. [ABSTRACT FROM AUTHOR]

The problem of the effect of inhomogeneous impurities in a lattice structure on the critical behaviour of systems which undergo a second-order phase transition is studied on a model system, the 2D Ising Model with impurity bonds randomly distributed over the lattice
It is known that in the critical region the 2D Ising Model is equivalent to the model of free fermions We show that the effect of impurities is to add a four-fermion interaction with the corresponding charge proportional to the concentration of impurities The resulting fermion model as sample enough and can be studied exactly by renormalization group methods We show that for any small concentration of impurity bonds a new critical regime is established if we go sufficiently close to the phase-transition point In particular we find that the specific heat singularity changes from C~In 1/||(=(T-T)/T), to C~ln ln 1/|| for ~ exp (-const/c), c being the concentration of impurities, while the spin-spin correlation function in the critical point changes more seriously from <óRóO>~l/R to <óRóO>~exp {-(const/c)(lnlnR)} for RR~exp(const/c), which corresponds to a change of the critical exponent from 1/4 to 0. [ABSTRACT FROM AUTHOR]

Under the assumption that the product of two spin operators decomposes uniquely into the degenerate conformal fields { Φ n ′ , n } , the general expression for the correlation function of four spins is defined for the q states Potts model with q taking general values in the interval 1 ≤ q ≤ 4. The limit of q → 1 is considered in detail and the four spin function is obtained for the percolation model. [ABSTRACT FROM AUTHOR]

We prove the conjectures on dimensions and characters of some quadratic algebras stated by B. L. Feigin. It turns out that these algebras are naturally isomorphic to the duals of the components of the bi-Hamiltonian operad. [ABSTRACT FROM PUBLISHER]

A software radio receiver that can be programmed to operate in multiple wide frequency bands is required for many communication and intelligence applications. We have designed a variety of multi-band receivers, comprising a set of band-specific analog-to-digital converters (ADCs) for direct digitization of RF bands and a digital switch matrix for band selection, in two flavors: as a single superconductor integrated circuit chip and also as a multi-chip module. In addition to the ADCs and the switch, these include a 1:16 deserializer and output drivers to facilitate transport of the digitized RF data to room temperature electronics for further processing and analysis. In the single IC flavor, up to four bandpass delta-sigma ADCs minimizing quantization noise in their respective bands were integrated on the same chip and operated at clock rates up to 20 GHz. In the multi-chip module (MCM) implementation, a 1-cm \times 1-cm universal active carrier was designed to accommodate any two 2.5-mm \times 2.5-mm flipped chips, each containing a single ADC front-end. This standardized approach facilitates customization of two-band ADCs by selecting from a growing library of ADC front-ends, which currently cover bands ranging from HF (0–30 MHz) to Ka-band (20–21 GHz). These Multi-band MCMs and single chip ADC's were fabricated, assembled and tested. [ABSTRACT FROM AUTHOR]

Superconductor digital receiver systems of increasing functionality, modularity and user-friendliness have been developed. The modular design methodology ensures that within its input-output and heat load capacity, the system can be reconfigured to perform a different function by changing the chip module and by reprogramming FPGA-based digital signal processors. One of the systems (ADR-004), originally equipped with a 10\times 10\ mm^2 channelizing receiver chip for signals intelligence application, was reconfigured with a 5\times 5\ mm^2 1.1-GHz bandpass ADC chip to perform world's first multi-net Link-16 demonstration at a U.S. Navy facility. Substantial improvements in system integration have been obtained in each successive generation of digital-RF receiver systems. The latest (third) generation system (ADR-005), hosting a 5\times 5\ mm^2 7.5-GHz bandpass ADC chip and an FPGA channelizer, successfully repeated the over-the-air SATCOM demonstration performed previously using a 1-cm^2 single-chip bandpass digital receiver with an on-chip superconductor channelizer. This system ran error-free for over 12 hours with and without a low-noise amplifier. To our knowledge, this is the first time an X-band SATCOM receiver has been operated without analog amplification and down-conversion in a military application. [ABSTRACT FROM AUTHOR]

We report the development of a nano-engineered cryogenic adhesive (nECA) consisting of an epoxy impregnated with single walled carbon nanotubes (SWNT) for bonding niobium-based superconductor multi-chip modules (MCMs). The nECA offers 300%–900% enhancement in thermal conduction over the base adhesive while maintaining high electrical resistivity. Additionally, we report the thermal modeling results for a niobium-based superconducting single chip module with the incorporation of pure epoxy and nECA. When the heat flow is exclusively through the In/Sn bumps the thermal model predicts > 100 mK temperature difference between the flipped chip with active circuitry and the passive carrier substrate, which might degrade the chip's performance and the operating margins. With the use of 0.1 wt% SWNT loaded epoxy as the underfill, we report reduction of temperature differences to a more acceptable level of \sim19 mK. These results are expanded to foreseeable MCM package designs to highlight the merit of nECA as an underfill material for superconducting electronic packages. [ABSTRACT FROM AUTHOR]

HYPRES is developing a class of digital receivers featuring direct digitization at radio frequency. The complete system, consisting of a cryopackaged Nb superconductor All-Digital Receiver (ADR) chip followed by room-temperature interface electronics and a field-programmable gate array (FPGA) based post-processing module, has been developed. Depending on the targeted application the ADR chip comprised either a low-pass delta with phase modulation-demodulation architecture or X-band band-pass sigma-delta modulators together with digital in-phase and quadrature mixer and a pair of digital decimation filters. The chips were fabricated using a 4.5-kA/cm2 HYPRES process and were cryopackaged using a commercial-off-the-shelf cryocooler. Recently, with significant improvements in chip cryopackage, room-temperature electronics and FPGA programming we were able to achieve stable operation of a low-pass ADR at 28.16 GHz and X-band ADR at 30.72 GHz clock frequencies. Experimental results are presented and discussed. [ABSTRACT FROM AUTHOR]

A series of tris(pyrazolyl)borate mono-, di- and trinuclear complexes, [Tp2Ln]nX (Ln = Eu, Tb, Gd, Dy, Xn− = various mono-, bis- and tris(β-diketonates) has been prepared. The Tb3+ and Dy3+ complexes are luminescent single molecular magnets (SMM) and exhibit luminescence quantum efficiencies up to 73% for the Tb3+ and 4.4% for the Dy3+ compounds. Similar Eu3+ complexes display bright emission only at lower temperatures. The Dy3+ and Tb3+ complexes possess SMM behavior in a non-zero dc field at low temperatures, while the polynuclear Dy3+ complexes also show slow magnetic relaxation even in zero dc field up to 8 K. Ueff-values determined from dynamic magnetic measurements were up to 31 and 6 cm−1 for the Dy3+ and Tb3+ complexes, respectively. It was found that within a series of Dy3+ and Tb3+ compounds, Ueff and luminescence quantum yields decreased with increasing nuclearity of the compounds and a shortening of the intramolecular Ln–Ln distance. ΔOrbach-values estimated from low-temperature luminescence spectra were significantly higher than those obtained from ac magnetic data, which may be due to involvement of additional processes in the relaxation mechanism (quantum tunneling, Raman, direct) reducing the energy barrier. Some of the Tb3+-compounds also display metal-centred electroluminescence, giving them potential as emitting layers in LEDs. [ABSTRACT FROM AUTHOR]

As the digital data links for superconducting circuits advance and higher data throughput per channel becomes possible, timing margins shrink and data integrity becomes a major challenge. Particular interest for multichannel applications is establishing the high-quality data link to interface with subsequent electronics. In this paper, we focus on integration of an on-chip pseudorandom binary sequence (PRBS) generator into a superconducting analog-to-digital converter (ADC) design to facilitate link stability evaluation and automated interchannel synchronization. PRBS generator and the ADC use a common clock source. An on-chip deserializer/demux, which includes the output drivers, is driven by a set of data sources depending on switch selections on-chip. The outputs are connected to a field-programmable gate array (FPGA) at room temperature, which hosts the developed interface circuitry for data reception, data integrity evaluation, and the synchronization mechanism. The integrated circuit (IC) that combines ADC and PRBS7 generator circuit was designed for the HYPRES 4.5 kA/cm2 four-layer standard fabrication process and features four deserialized outputs. A second similar IC was designed comprising an ADC frontend as well as a PRBS15 generator and was fabricated in the MIT-LL 10 kA/cm2 process. The implemented alignment engine that bonds the individual channels into a single data link was proven up to 10 Gbps while taking 1–2 μs to complete the alignment. We built chip-to-FPGA data links, comprising the on-chip driver and room-temperature interface amplifier, up to 14 Gbps using FPGA serial-link GTY transceiver. Successful data transport from an ADC using multiple parallel data links to an FPGA upon completion of the channel bonding was demonstrated. [ABSTRACT FROM PUBLISHER]

Efficiently amplifying the high-speed and low-voltage swing outputs of single flux quantum (SFQ) logic to levels that are suitable for interfacing with room temperature electronics has been a long-standing challenge in the field of superconducting electronics. In this work, we investigate the feasibility of using a lossy passive matching network at 4 K, with a pair of differential 100 low-noise amplifiers heatsunk to 18 K and 50 K stages, respectively. The amplifiers were implemented in a 120 nm SiGe BiCMOS technology. The amplification chain is dc coupled and the small-signal link gain was measured to be approximately 48 dB. The power consumption of each of the two amplification stages was 6.3 mW. The chain was measured at 21 K using a high-speed differential nonreturn-to-zero signal having amplitude commensurate with what one would expect from a superconducting circuit, and clean eye diagrams were observed for data rates as high as 30 Gb/s. The chain was also measured when driven from an SFQ/dc interface, with the first gain stage heatsunk to 9 K. In this configuration, clean eye diagrams were observed to 5 Gb/s, with the speed limitation being related to packaging parasitics. [ABSTRACT FROM PUBLISHER]

A series of brightly luminescent new mononuclear TpPyLn(An)2(H2O) (where An− = carboxylate anion, Ln = Eu or Tb and TpPy− = tris(3-(2′-pyridyl)pyrazolyl)borate) and dinuclear (TpPyLn)2pma(MeOH)2 (Ln = Eu, Tb, pma4− = tetraanion of pyromellitic acid) complexes were prepared and characterized by X-ray crystallography. Within each series the compounds possess similar molecular structures, which differ only by the nature of the carboxylate anions. The quantum efficiencies for metal-centered emission of the complexes were up to 29(3)% for Eu3+ and 53(5)% for the Tb3+ compounds and significantly depend on the electronic structure of the additional ligand (i.e. the carboxylate). The aliphatic carboxylate compounds’ luminescence quantum yields were all similar, but different from those for the aromatic ones. The complexes with trifluoroacetate and pentafluorobenzoate unexpectedly displayed lower quantum efficiencies compared to those with the corresponding non-fluorinated analogues. Energy transfer from Tb3+ to Eu3+ occurs in a mixture of (TpPyEu)(pma)(TbTpPy)(MeOH)2, (TpPyEu)2(pma)(MeOH)2 and (TpPyTb)2(pma)(MeOH)2 but is not very efficient. The Tb3+-compounds displayed green electroluminescence, and both the Eu3+ and Tb3+ complexes exhibited bright metal-centered red (Eu3+) or green (Tb3+) triboluminescence. [ABSTRACT FROM AUTHOR]

Interfacing superconducting rapid single flux quantum logic with room temperature electronics requires the development of low-power semiconductor circuitry capable of operating at tens of Gb/s while maintaining sufficient signal to noise to achieve acceptable bit-error-rates. Such data-links must operate with sufficiently low power consumption to permit tens to hundreds of parallel channels to coexist in a single cryostat. This requires a careful trade-off between the power and noise performance of the cryogenically cooled digital amplifiers. Previously demonstrated ultra low-power cryogenic-to-room temperature digital data links have been limited to data rates on the order of a few Gb/s. In this paper we demonstrate a temperature distributed amplifier chain optimized for 30 Gb/s data transmission and consuming just 140 microwatts at 4 K. [ABSTRACT FROM PUBLISHER]

The luminescense properties of Ce3+ ions in Ca 2 BO 3 Cl were studied upon excitation in the 3–20 eV range. It is shown that because of the presence of different charge compensating defects, the various types of centers involving Ce3+ are formed in Ca 2 BO 3 Cl. Based on the results obtained, the values of the crystal field splitting and the centroid shift of the Ce3+ 5d configuration for locally uncompensated Ce3+ centers were determined and compared with those of Ce3+ ions in some other inorganic compounds. The DFT calculations were utilized to study the band structure of Ca 2 BO 3 Cl, the 4f→5d transitions of Ce3+ ions and the intrinsic defects of this compound. The calculated band gap of Ca 2 BO 3 Cl (7.22 eV) is consistent with the experimental value of 7.35 eV, and the 4f→5d transition energies for Ce3+ ions on the two sevenfold coordination sites confirm spectral assignments based on the luminescent measurements. The experimental results and first-principles calculations show that the introduction of Na+ hardly influences the luminescence properties of Ce3+-doped Ca 2 BO 3 Cl. The possible processes occurring in Ca 2 BO 3 Cl:Eu2+, Ce3+ persistent phosphors are also discussed based on the combined theoretical and experimental results. • Several types of Сe3+-related centers are observed. • At low Ce3+ concentrations, locally uncompensated Ce3+ centers prevail. • The calculated band gap of Ca 2 BO 3 Cl agrees with the experimental value of 7.35 eV. • VRBE diagram implies the involvement of the CB in the PersL charging process. [ABSTRACT FROM AUTHOR]