Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Quantum communication without alignment using multiple-qubit
  single-photon states   We propose a scheme for encoding logical qubits in a subspace protected
against collective rotations around the propagation axis using the polarization
and transverse spatial degrees of freedom of single photons. This encoding
allows for quantum key distribution without the need of a shared reference
frame. We present methods to generate entangled states of two logical qubits
using present day down-conversion sources and linear optics, and show that the
application of these entangled logical states to quantum information schemes
allows for alignment-free tests of Bell's inequalities, quantum dense coding
and quantum teleportation.

14
The categories of this paper are: math-ph
6
The categories of this paper are: astro-ph
4
The categories of this paper are: cond-mat
7
The categories of this paper are: hep-th
32
The categories of this paper are: atom-ph
12
The categories of this paper are: nucl-th
34
The categories of this paper are: chem-ph
35
The categories of this paper are: mtrl-th
24
The categories of this paper are: dg-ga
16
The categories of this paper are: stat
9
The categories of this paper are: nlin
27
The categories of this paper are: comp-gas
25
The categories of this paper are: patt-sol
18
The categories of this paper are: econ
33
The categories of this paper are: plasm-ph
20
The categories of this paper are: acc-phys