We give a mathematical formulation for the Choi-Jamiolkowski (CJ) correspondence in the infinite-dimensional case in the form close to one used in quantum information theory. We show that there is no need to use a limiting procedure to define unnormalized maximally entangled state and the corresponding analog of the Choi matrix since they can be defined rigorously as, in general, nonclosable forms on an appropriate dense subspace. The properties of these forms are discussed in Sec. 2. An important question is: when the CJ form is given by a bounded operator. This is the case for entanglement-breaking channels: we prove this in Sec. 3 along with a version of a result of Wolf et al. characterizing CJ operators which correspond to such channels by giving precise definitions of a separable operator and a relevant integral. In Sec. 4 we obtain explicit expressions for CJ forms and operators defining a general Bosonic Gaussian channel. In Sec. 5 we give a decomposition of the Gaussian CJ form into product of the four principal types and a necessary and sufficient condition for existence of the bounded CJ operator.
A generalization of the Choi-Jamiolkowski isomorphism for completely positive maps between operator algebras is introduced. Particular emphasis is placed on the case of normal unital completely positive maps defined between von Neumann algebras. This generalization is applied especially to the study of maps which are covariant under actions of a symmetry group. We highlight with the example of, e.g., phase-shift-covariant quantum channels the ease of this method in particular in the case of a compact symmetry group. We also discuss the case of channels which are covariant under actions of the Euclidean group of rigid motions in 3 dimensions.
Abstract A structure theorem is established which shows that an arbitrary multimode bosonic Gaussian observable can be represented as a combination of four basic cases whose physical prototypes are homodyne and heterodyne, noiseless or noisy, measurements in quantum optics. The proof establishes a connection between the descriptions of a Gaussian observable in terms of the characteristic function and in terms of the density of a probability operator-valued measure (POVM) and has remarkable parallels with the treatment of bosonic Gaussian channels in terms of their Choi–Jamiołkowski form. Along the way we give the “most economical” (in the sense of minimal dimensions of the quantum ancilla) construction of the Naimark extension of a general Gaussian observable. We also show that the Gaussian POVM has bounded operator-valued density with respect to the Lebesgue measure if and only if its noise covariance matrix is nondegenerate.
Provided a maximally entangled state vector in
H⊗H, the Choi-Jamiolkowski isomorphism of quantum information theory (or channel/state duality) produces a mapping of
CP(H,K) (completely positive maps of density operators on
H tothose on
K) onto the density operators on
K⊗H, which extends to a unitary map. Here,
H and
K are {finite-dimensional} Hilbert spaces.The nature of this construction, the form of the associated formulas, and the possibility of versions which do not require an entangled vector seed, are illuminated from the perspective of {naturality}, in the sense of Eilenberg and MacLane.There is a unique such correspondence (``Choi map'') natural in both
H and
K which produces density operators on either
L(H,K) (Hilbert-Schmidt inner product) or
K⊗H∗ instead of
K⊗H. In particular, no entangled state input is required. There are no such binatural maps carried on
K⊗H, but those natural in only
K are canonically associated with unitary maps
H→H∗ and derive from the binatural maps. The construction recovers the standard Choi-Jamiolkowski formulae and shows how they express naturality.
A general quantum channel can be represented in terms of a unitary interaction between the information-carrying system and a noisy environment. In this paper the minimal number of quantum Gaussian environmental modes required to provide a unitary dilation of a multimode bosonic Gaussian channel is analyzed for both pure and mixed environments. We compute this quantity in the case of pure environment corresponding to the Stinespring representation and give an improved estimate in the case of mixed environment. The computations rely, on one hand, on the properties of the generalized Choi-Jamiolkowski state and, on the other hand, on an explicit construction of the minimal dilation for arbitrary bosonic Gaussian channel. These results introduce a new quantity reflecting ``noisiness'' of bosonic Gaussian channels and can be applied to address some issues concerning transmission of information in continuous variables systems.
We present a complete characterization of quantum channels covariant under the action of SU(2), a symmetry that arises naturally across a wide range of physical settings. By exploiting the constraints imposed by rotational symmetry, we derive the spectral decomposition of the associated Choi–Jamiołkowski operators and obtain explicit closed-form expressions for the corresponding Kraus operators. This unified framework provides a systematic approach to analyzing the structure and dynamics of SU(2)-covariant noise, with direct applications to quantum communication, information processing, and symmetry-constrained quantum protocols.