Proposed Test of Quantum Nonlocality for Continuous Variables

Abstract

We propose a test of nonlocality for continuous variables using a two-mode squeezed state as the source of nonlocal correlations and a measurement scheme based on conditional homodyne detection. Both the CHSH-and the CH-inequality are constructed from the conditional homodyne data and found to be violated for a squeezing parameter larger than r ≈ 0.48.

Persistent entanglement in the classical limit

“…The dependence of the entropy of entanglement on β is similar in form for both unravellings (one continuous and one discontinuous). We find, as might be expected [18], that the entropy of entanglement for quantum jumps differs from that of QSD. However, even though the average level differs between unravellings, the behaviour of the average entanglement, both chaotic-like and nonchaotic, as a function of β is very similar.…”

“…This unravelling makes assumptions about the underlying measurement process which is applied to the environment: unit efficiency heterodyne detection for QSD. However, studies have shown that the level of entanglement is dependent upon which unravelling is used [18]. It is natural then to ask whether the properties of the entanglement that we have described above are particular to the QSD unravelling.…”

Conditional generation of an arbitrary superposition of coherent states

“…The progress of these experiments promises the realizations of more complicated applications of photon subtraction proposed so far, including the improvement of quantum teleportation [7,8,9] and entanglement-assisted coding [10], entanglement distillation [11], loophole free tests of Bell's inequalities [12,13,14], and optical quantum computations in quadrature basis [15,16] or superposed coherent state basis [17,18]. In the last application, |C ± (α) with appropriate α is required as an ancillary state.…”

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

“…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].…”