Light-matter quantum interface

We propose a quantum interface which applies multiple passes of a pulse of light through an atomic sample with phase/polarization rotations in between the passes. Our proposal does not require nonclassical light input or measurements on the system, and it predicts rapidly growing entanglement of light and atoms from just coherent inputs. The proposed interface makes it possible to achieve a number of tasks within quantum-information processing, including teleportation between light and atoms, quantum memory for light, and squeezing of atomic and light variables.

Figure 1

GEOF and EPR variance vs number of passes: For given $n$ both quantities are maximized with respect to $\eta$ and $\zeta$. The optimal values for $\eta$ are shown in the insets. It is always best to have $\zeta =r$ corresponding to $ϵ⪡\eta$. $(+)$ refers to the case $r=0$, $(\times )$ to $r=2\%$. The optical density is ${\alpha }_0=25$.

Figure 2

GEOF and EPR variance vs number of passes including polarization rotations: $(+)$ refers to the case $r=0$, $(\times )$ to $r=2\%$. Optical density ${\alpha }_0=25$.

Figure 3

Atomic squeezing after homodyne detection of light: Unswitched scheme (QND measurement) $“+”$ and switched scheme $“\times .”$ $\zeta =r=2\%$, ${\alpha }_0=25$.

Figure 4

Squeezing of light $(+)$ and atomic $(\times )$ quadrature after $n$ entangling and a single disentangling step. The results from a comparable QND measurement on the atomic system “엯.” $\zeta =r=2\%$, ${\alpha }_0=25$. Inset: the optimal value for coupling ${\kappa }_{opt}={\alpha }_0{\eta }_{opt}$ and theoretical magical value ${\kappa }_0=\sqrt{n-1∕2}∕n$ (solid line). Atomic depumping $\eta$ decreases with $\kappa$, while light suffers a constant loss of 2% per pass. Therefore, the asymmetry in squeezing of light an atomic variables.