The s-ordered form of any product of single-mode boson creation and annihilation operators, containing only a single annihilator, is computed explicitly. The s-ordering concept originated in quantum optics, but subsumes normal, symmetric (Weyl), and anti-normal ordering for any two operators satisfying a canonical commutation relation. Because the s-ordering map can be viewed as producing a function of a complex variable, its inverse is a quantization map that takes such “classical” functions to quantum operators. The explicit s-ordered expressions are derived with the aid of a parametric family of Sheffer polynomial sequences (or equivalently a parametric exponential Riordan array of polynomial coefficients), called the Hsu–Shiue family. To yield orderings interpolating between normal and anti-normal, this family must be extended.
We solve the boson normal ordering problem for ( q ( a † ) a + v ( a † )) n with arbitrary functions q ( x ) and v ( x ) and integer n , where a and a † are boson annihilation and creation operators, satisfying [ a , a † ] = 1. This consequently provides the solution for the exponential e λ( q ( a † ) a + v ( a † )) generalizing the shift operator. In the course of these considerations we define and explore the monomiality principle and find its representations. We exploit the properties of Sheffer-type polynomials which constitute the inherent structure of this problem. In the end we give some examples illustrating the utility of the method and point out the relation to combinatorial structures.
In reference to the Weyl ordering , where X and P are coordinate and momentum operator, respectively, this paper examines operators' s -parameterized ordering and its classical correspondence, finds the fundamental function-operator correspondence and its complementary relation where H m,n is the two-variable Hermite polynomial, a , a † are bosonic annihilation and creation operators respectively, s ′ is a complex parameter. The s -ordered operator power-series expansion of s -ordered operator in terms of the two-variable Hermite polynomial is also derived. Application of operators' s -ordering formula in studying displaced-squeezed chaotic field is discussed.
The structure of ordered expansions in powers of boson operators and of canonical operators and the dual problem of operator reconstruction from ordered moments is derived and applied to the complete Gaussian class of ordering. In particular, the interpolation lines between normal and antinormal ordering and between standard and antistandard ordering with Weyl symmetrical ordering in their centre are dealt with in detail. The auxiliary operators for expansions in symmetrical ordering are explicitly found in the Fock-state representation and in other different representations. General and specialized formulae are derived for different ordering of powers of linear combinations of boson and of canonical operators which involve Hermite polynomials of operators. The link between symmetrical ordering of powers of boson operators and of canonical operators is expressed by means of Jacobi polynomials. Some basic formulae of operator ordering and operator expansion are collected for convenient use in the appendix.
The expansion of operators as ordered power series in the annihilation and creation operators
a and ${a}^{\ifmmode\dagger\else\textdagger\fi{}}$ is examined. It is found that normally ordered power series exist and converge quite generally, but that for the case of antinormal ordering the required
c-number coefficients are infinite for important classes of operators. A parametric ordering convention is introduced according to which normal, symmetric, and antinormal ordering correspond to the values $s=+1,0,\ensuremath{-}1$, respectively, of an order parameter
s. In terms of this convention it is shown that for bounded operators the coefficients are finite when
s>0, and the series are convergent when
s>21. For each value of the order parameter
s, a correspondence between operators and
c-number functions is defined. Each correspondence is one-to-one and has the property that the function $f(\ensuremath{\alpha})$ associated with a given operator
F is the one which results when the operators
a and ${a}^{\ifmmode\dagger\else\textdagger\fi{}}$ occurring in the ordered power series for
F are replaced by their complex eigenvalues $\ensuremath{\alpha}$ and ${\ensuremath{\alpha}}^{*}$. The correspondence which is realized for symmetric ordering is the Weyl correspondence. The operators associated by each correspondence with the set of $\ensuremath{\delta}$ functions on the complex plane are discussed in detail. They are shown to furnish, for each ordering, an operator basis for an integral representation for arbitrary operators. The weight functions in these representations are simply the functions that correspond to the operators being expanded. The representation distinguished by antinormal ordering expresses operators as integrals of projection operators upon the coherent states, which is the form taken by the
P representation for the particular case of the density operator. The properties of the full set of representations are discussed and are shown to vary markedly with the order parameter
s.
The problem of quantizing a bivariate dynamical system can be reduced to evaluating the ordering of
q^jp^k. Here, we consider the Weyl ordering of
q^jp^k that is then expressed in term of the annihilation
a^ and creation
a^† operator. The explicit formula for the normal-ordered equivalent (all
a^†'s preceeding all
a^'s) of the resulting expression is then given, and some relations are discussed.