Enhancing quantum entanglement by photon addition and subtraction

Abstract

The non-Gaussian operations effected by adding or subtracting a photon on the entangled optical beams emerging from a parametric down-conversion process have been suggested to enhance entanglement. Heralded photon addition or subtraction is, as a matter of fact, at the heart of continuous-variable entanglement distillation. The use of such processes has recently been experimentally demonstrated in the context of the generation of optical coherent-state superpositions or the verification of the canonical commutation relations. Here, we carry out a systematic study of the effect of local photon additions or subtractions on a two-mode squeezed vacuum state, showing that the entanglement generally increases with the number of such operations. This is analytically proven when additions or subtractions are restricted to one mode only, while we observe that the highest entanglement is achieved when these operations are equally shared between the two modes. We also note that adding photons typically provides a stronger entanglement enhancement than subtracting photons, while photon subtraction performs better in terms of energy efficiency. Furthermore, we analyze the interplay between entanglement and non-Gaussianity, showing that it is more subtle than previously expected.Comment: 10 pages, 6 figure

Entropy generation in Gaussian quantum transformations: applying the replica method to continuous-variable quantum information theory

“…The reduced output stateρ m of the signal mode is diagonal in the Fock basis, with a vector of eigenvalues given by 18,21 …”

Quantum state engineering by click counting

“…Another prominent example for controlled state manipulation is noiseless amplification [43][44][45][46][47]. All these engineering processes are able to enhance quantum properties, such as entanglement, for applications in quantum information science, see, e.g., [48][49][50][51][52][53][54][55][56][57][58].…”

Increasing and decreasing entanglement characteristics for continuous variables by a local photon subtraction

“…Other coherent superposition operations, such as tâ+rb † and tââ † +râ †â , were also proposed to produce an arbitrary photon-number entangled state in a finite dimension, N n=0 c n |n, n AB [42]. Due to the fact that entanglement characteristics of Gaussian states are enhanced by a non-Gaussian operation [9][10][11][12][13][14][15][16][17][18][19][20][21], it is natural to have a question about whether entanglement characteristics of non-Gaussian states are enhanced by a non-Gaussian operation. In particular, we are interested in non-Gaussian states which do not have any two-mode squeezing properties in order to determine their own usefulness compared with a typical Gaussian entangled state.…”

“…Some of us have recently proposed entanglement criteria beyond the Gaussian regime, where the entanglement criteria including all orders of EPR correlations can be measured with homodyne detection [8]. Non-Gaussian entangled states provide the benefits on enhancing violation of Bell's inequality [9][10][11], and degree of entanglement [12][13][14][15][16][17][18][19][20][21].…”