Squeezed spin states possess unique quantum correlation or entanglement that are of significant promises for advancing quantum information processing and quantum metrology. In recent back to back publications [C. Gross et al, Nature 464, 1165 and Max F. Riedel et al, Nature 464, 1170Nature 464, (2010], reduced spin fluctuations are observed leading to spin squeezing at −8.2dB and −2.5dB respectively in two-component atomic condensates exhibiting one-axis-twisting interactions (OAT). The noise reduction limit for the OAT interaction scales as ∝ 1/N 2/3 , which for a condensate with N ∼ 10 3 atoms, is about 100 times below standard quantum limit. We present a scheme using repeated Rabi pulses capable of transforming the OAT spin squeezing into the two-axis-twisting type, leading to Heisenberg limited noise reduction ∝ 1/N , or an extra 10-fold improvement for N ∼ 10 3 .PACS numbers: 42.50.-p, 03.75.GgSqueezed spin states (SSS) [2,3] are entangled quantum states of a collection of spins in which the correlations among individual spins reduce quantum uncertainty of a particular spin component below the classical limit for uncorrelated particles [2]. Research in SSS is a topical area due to its significant applications in high-precision measurements [3][4][5][6][7][8][9][10] and in quantum information science [11][12][13][14][15]. Squeezed spin states were first introduced by Kitagawa and Ueda, who considered two ways to produce them. The simplest to implement uses a "one-axis twisting" (OAT) Hamiltonian, but the state it produces does not have ideal squeezing properties. A more complex approach uses a "two-axis twisting" (TAT) Hamiltonian and produces an improved state. Other mechanisms for producing SSS have also been investigated, especially those based on atom-photon interactions [16,17] and quantum non-demolition measurements [18][19][20][21].Atomic Bose-Einstein condensates are promising systems for observing spin squeezing. Assuming fixed spatial modes, condensed atoms are described by a collection of pseudo-spin 1/2 atoms, with spin up (|↑ ) and down (|↓ ) denoting the two internal states or spatial modes [12,[22][23][24][25]. The two recent experiments [4, 5] raise significant hope for reaching the theoretical limit of spin squeezing ∝ 1/N 2/3 with N the total number of atoms for the OAT model [2]. Both experiments utilize two internal hyperfine states of condensed atoms, with the OAT interaction cleverly constructed from binary atomic collisions, possibly accompanied by systematic and fundamental imperfections not confined to the two state/mode approximation. They can be further degraded by atomic decoherence and dissipation [4,5]. This Letter describes a readily implementable idea for improved spin squeezing in the two experiments. Given the reported OAT model parameters [4,5], we propose a coherent control scheme capable of transforming the OAT into the effective TAT spin squeezing, leading to a Heisenberg limited noise reduction ∝ 1/N , or a further 10 fold improvement for a condensate with ∼ 10 3 at...

Including collisional decoherence explicitly, phase sensitivity for estimating effective scattering strength $\chi$ of a two-component Bose-Einstein condensate is derived analytically. With a measurement of spin operator $\hat{J}_{x}$, we find that the optimal sensitivity depends on initial coherent spin state. It degrades by a factor of $(2\gamma)^{1/3}$ below super-Heisenberg limit $\propto 1/N^{3/2}$ for particle number $N$ and the dephasing rate $1<\!<\gamma

Quantum transport properties of two-dimensional electron gas (2DEG) in undoped Mg x Zn 1Àx O/ZnO heterostructures grown by metal organic vapor phase epitaxy have been investigated. A large zero-field spin-splitting energy more than 15 meV in the 2DEG is determined at 1.6 K. Meanwhile, ferromagnetism is observed in the heterostructures. The findings reveal that the 2DEG is spin polarized at zero magnetic fields. It is believed that the exchange interaction between the itinerant electrons in the two-dimensional channel and the magnetic polarons in the Mg x Zn 1Àx O barrier around the interface results in the spin polarization of the 2DEG. V

Based upon standard angular momentum theory, we develop a framework to investigate polarization squeezing and multipartite entanglement of a quantum light field. Both mean polarization and variances of the Stokes parameters are obtained analytically, with which we study recent observation of triphoton states [L. K. Shalm {\it et al}, Nature \textbf{457}, 67 (2009)]. Our results show that the appearance of maximally entangled NOON states accompanies with a flip of mean polarization and can be well understood in terms of quantum Fisher information.Comment: 5 pages, 3 figures, to be published in the Quantum Optical Information Technology feature issue of JOSA B

ZnO nanotetrapods were prepared by hydrothermal emulsion method. The X-ray diffraction result showed the hexagonal wurtzite structure of the ZnO nanotetrapods. The main morphology of the ZnO whiskers is a nanotetrapod, aside from the sheet- and flower-shaped ZnO. Growth time and cyclohexane dosage exert some influences on the morphology and size of ZnO. In addition, aluminum doping plays an important role on the morphology of ZnO.