arXiv subjects

Yaping Yang

Publications and source records attributed to Yaping Yang.

48 records · Page 3Linked to original sources

arXiv2018

Electromagnetic control of nonclassicality in cavity QED system

We present a study of the electromagnetic control of nonclassicality of the outgoing light field in a single atom cavity QED system. By exploring the energy eigenvalues and eigenstates, we show that the eigenstates are similar to the Jaynes-Cummings ladder of eigenstates and can be optically controlled by an external control field. Tuning the control field frequency to the one photon resonance, we show the superbunching behavior in the outgoing light field can be observed at the frequency of one photon resonance. We also show that there exists a magic control field intensity at which two photon blockade phenomenon can be significantly improved. In particular, it is possible to adjust the nonclassicality of the outgoing field from quantum to classical by varying the control field intensity. The work presented here provides an optical method to control statistical features of the outgoing field and can be useful for the nonclassical light generation, quantum gate operation and exotic quantum state generation.

quant-ph↗

arXiv2018

The PBW theorem for the affine Yangians

We prove that the Yangian associated to an untwisted symmetric affine Kac-Moody Lie algebra is isomorphic to the Drinfeld double of a shuffle algebra. The latter is constructed by the authors in arXiv:1407.7994 as an algebraic formalism of the cohomological Hall algebras. As a consequence, we obtain the Poincare-Birkhoff-Witt (PBW) theorem for this class of affine Yangians. Another independent proof of the PBW theorem is given recently by Guay-Regelskis-Wendlandt.

math.RT↗

arXiv2018

How to sheafify an elliptic quantum group

We give an introductory survey of the results in arXiv: 1708.01418. We discuss a sheafified elliptic quantum group associated to any symmetric Kac-Moody Lie algebra. The sheafification is obtained by applying the equivariant elliptic cohomological theory to the moduli space of representations of a preprojective algebra. By construction, the elliptic quantum group naturally acts on the equivariant elliptic cohomology of Nakajima quiver varieties. As an application, we obtain a relation between the sheafified elliptic quantum group and the global affine Grassmannian over an elliptic curve.

math.RT↗

arXiv2018

Universal KZB Equations for arbitrary root systems

Generalising work of Calaque-Enriquez-Etingof, we construct a universal KZB connection D_R for any finite (reduced, crystallographic) root system R. D_R is a flat connection on the regular locus of the elliptic configuration space associated to R, with values in a graded Lie algebra t_R with a presentation with relations in degrees 2, 3 and 4 which we determine explicitly. The connection D_R also extends to a flat connection over the moduli space of pointed elliptic curves. We prove that its monodromy induces an isomorphism between the Malcev Lie algebra of the elliptic pure braid group P_R corresponding to R and t_R, thus showing that P_R is not 1-formal and extending a result of Bezrukavnikov valid in type A. We then study one concrete incarnation of our KZB connection, which is obtained by mapping t_R to the rational Cherednik algebra H_{h,c} of the corresponding Weyl group W. Its monodromy gives rise to an isomorphism between appropriate completions of the double affine Hecke algebra of W and H_{h,c}.

math.AT↗

arXiv2017

The cohomological Hall algebra of a preprojective algebra

We introduce for each quiver $Q$ and each algebraic oriented cohomology theory $A$, the cohomological Hall algebra (CoHA) of $Q$, as the $A$-homology of the moduli of representations of the preprojective algebra of $Q$. This generalizes the $K$-theoretic Hall algebra of commuting varieties defined by Schiffmann-Vasserot. When $A$ is the Morava $K$-theory, we show evidence that this algebra is a candidate for Lusztig's reformulated conjecture on modular representations of algebraic groups. We construct an action of the preprojective CoHA on the $A$-homology of Nakajima quiver varieties. We compare this with the action of the Borel subalgebra of Yangian when $A$ is the intersection theory. We also give a shuffle algebra description of this CoHA in terms of the underlying formal group law of $A$. As applications, we obtain a shuffle description of the Yangian.

math.RT↗

arXiv2017

Cohomological Hall algebras and affine quantum groups

We study the preprojective cohomological Hall algebra (CoHA) introduced by the authors in an earlier work for any quiver $Q$ and any one-parameter formal group $\mathbb{G}$. In this paper, we construct a comultiplication on the CoHA, making it a bialgebra. We also construct the Drinfeld double of the CoHA. The Drinfeld double is a quantum affine algebra of the Lie algebra $\mathfrak{g}_Q$ associated to $Q$, whose quantization comes from the formal group $\mathbb{G}$. We prove, when the group $\mathbb{G}$ is the additive group, the Drinfeld double of the CoHA is isomorphic to the Yangian.

math.RT↗

arXiv2017

Quiver varieties and elliptic quantum groups

We define a sheafified elliptic quantum group for any symmetric Kac-Moody Lie algebra. This definition is naturally obtained from the elliptic cohomological Hall algebra of a preprojective algebra. The sheafified elliptic quantum group is an algebra object in a certain monoidal category of coherent sheaves on the colored Hilbert scheme of an elliptic curve. We show that the elliptic quantum group acts on the equivariant elliptic cohomology of Nakajima quiver varieties. This action is compatible with the action induced by Hecke correspondence, a construction similar to that of Nakajima. The elliptic Drinfeld currents are obtained as generating series of certain rational sections of the sheafified elliptic quantum group. We show that the Drinfeld currents satisfy the commutation relations of the dynamical elliptic quantum group studied by Felder and Gautam-Toledano Laredo.

math.RT↗

arXiv2016

On deformed double current algebras for simple Lie algebras

We prove the equivalence of two presentations of deformed double current algebras associated to a complex simple Lie algebra, the first one obtained via a degeneration of affine Yangians while the other one naturally appeared in the construction of the elliptic Casimir connection. We also construct a specific central element of these algebras and, in type A, show that they contain a very large center for certain values of their parameters.

math.QA↗

arXiv2016

Algebraic elliptic cohomology theory and flops, I

We define the algebraic elliptic cohomology theory coming from Krichever's elliptic genus as an oriented cohomology theory on smooth varieties over an arbitrary perfect field. We show that in the algebraic cobordism ring with rational coefficients, the ideal generated by differences of classical flops coincides with the kernel of Krichever's elliptic genus. This generalizes a theorem of B. Totaro in the complex analytic setting.

math.AG↗

arXiv2015

Homological finiteness of abelian covers

We present a method for deciding when a regular abelian cover of a finite CW-complex has finite Betti numbers. To start with, we describe a natural parameter space for all regular covers of a finite CW-complex X, with group of deck transformations a fixed abelian group A, which in the case of free abelian covers of rank r coincides with the Grassmanian of r-planes in H^1(X,\Q). Inside this parameter space, there is a subset Ω_A^i(X) consisting of all the covers with finite Betti numbers up to degree i. Building on work of Dwyer and Fried, we show how to compute these sets in terms of the jump loci for homology with coefficients in rank 1 local systems on X. For certain spaces, such as smooth, quasi-projective varieties, the generalized Dwyer-Fried invariants that we introduce here can be computed in terms of intersections of algebraic subtori in the character group. For many spaces of interest, the homological finiteness of abelian covers can be tested through the corresponding free abelian covers. Yet in general, abelian covers exhibit different homological finiteness properties than their free abelian counterparts.

math.GT↗

arXiv2012

Intersections of translated algebraic subtori

We exploit the classical correspondence between finitely generated abelian groups and abelian complex algebraic reductive groups to study the intersection theory of translated subgroups in an abelian complex algebraic reductive group, with special emphasis on intersections of (torsion) translated subtori in an algebraic torus.

math.GR↗

arXiv2008

Repulsive and restoring Casimir forces with left-handed materials

We investigate repulsive Casimir force between slabs containing left-handed materials with controllable electromagnetic properties. The sign of Casimir force is determined by the electric and magnetic properties of the materials, and it is shown that the formation of the repulsive force is related to the wave impedances of two slabs. The sign change of the Casimir force as a function of the distance is studied. Special emphasis is put on the restoring Casimir force which may be found to exist between perfectly conducting material and metamaterial slabs. This restoring force is a natural power for the system oscillation in vacuum and also can be used for system stabilization.

quant-ph↗