Algorithmic cooling based on cross-relaxation and decoherence-free subspace

Heat-bath algorithmic cooling(HBAC)has been proven to be a powerful and effective method for obtaining high polarization of the target system.Its cooling upper bound has been recently found using a specific algorithm,the partner pairing algorithm(PPAHBAC).It has been shown that by including cross-relaxation,it is possible to surpass the cooling bounds.Herein,by combining cross-relaxation and decoherence-free subspace,we present a two-qubit reset sequence and then generate a new algorithmic cooling(AC)technique using irreversible polarization compression to further surpass the bound.The proposed two-qubit reset sequence can prepare one of the two qubits to four times the polarization of a single-qubit reset operation in PPA-HBAC for low polarization.When the qubit number is large,the cooling limit of the proposed AC is approximately five times as high as the PPA-HBAC.The results reveal that cross-relaxation and decoherence-free subspace are promising resources to create new AC for higher polarization.

Exploring luminescence quenching on lanthanide-doped nanoparticles through changing the spatial distribution of sensitizer and activator

Luminescence quench is common in overdoped upconversion nanoparticles.Various methods have been proposed to counteract the adverse effects of concentration quenching on luminescence,but in upconversion nanoparticles that are highly doped with both sensitizers and activators,the factors that contribute to the diminishing of the emission cannot be summarized by a single cause.Herein,a core-shell design is used to spatially separate the sensitizer(Yb^(3+))and activator(Er^(3+))and to modulate the emission by changes in the distribution position as well as the concentration of the dopant ions in order to probe the factors affecting the luminescence.When the sensitizer ions are located in the core,the luminescence intensity of the nanoparticles is significantly weaker than that of the other distribution,which implies that the effect of sensitizer and activator on luminescence in the highly doped state has a different and more complex mechanism.The intensity of the emission is more affected by Yb^(3+)than Er^(3+),which includes not only the self-quenching of Yb^(3+),but also the dominance in the Yb^(3+)-Er^(3+)cross-relaxation.In this finding may provide new ideas for revealing the reasons for the diminished luminescence of highly doped upconversion nanoparticles and thus for enhancing luminescence.

Enhancement of red to orange emission ratio of YPO_4:Eu^(3+),Ce^(3+) and its dependence on Ce^(3+) concentration

Eu3＋ and Ce3＋ co-doped YPO4 microspheres were synthesized by hydrothermal method without template. The emission spectra showed that the red emission centered at 618nm could be readily increased relatively to the orange emission centered at 590nm by controlling the doping concentration of Ce3＋ ion. The investigation based on excitation spectra and decay curves demonstrated that the doped Ce3＋ ions took two efficient energy transfers to Eu3＋ ions and affected the lifetime of the emission states of Eu3＋ ions so that the emission spectra of Eu3＋ ion were accordingly tuned with the Ce3＋ content increasing. This controllable red （5D0→7F2） to orange （ 5D0→7F1） emission ratio of YPO4：Eu3＋,Ce3＋ made it very promising for encoded anti-fake labels and bio-labels.

UV/VUV switch-driven color-reversal effect for Tb-activated phosphors

The remarkable narrow-band emission of trivalent lanthanide-doped phosphors excited by the vacuum ultraviolet(VUV)radiation lines of Xe atoms/Xe_(2) molecules at 147/172 nm are extensively investigated in the development of plasma display panels and Hg-free fluorescent lamps,which are frequently used in our daily lives.Numerous solid materials,particularly Tb^(3+)-doped oxides,such as silicates,phosphates and borates,are efficient green/blue sources with color-tunable properties.The excitation wavelength and rare earth concentration are usually varied to optimize efficiency and the luminescent properties.However,some underlying mechanisms for the shift in the emission colors remain unclear.The present study shows that a UV/VUV switch systematically controls the change in the phosphor(Ba_(3)Si_(6)O_(12)N_(2):Tb)photoluminescence from green to blue,resulting in a green emission when the system is excited with UV radiation.However,a blue color is observed when the radiation wavelength shifts to the VUV region.Thus,a configurational coordinate model is proposed for the color-reversal effect.In this model,the dominant radiative decay results in a green emission under low-energy UV excitation from the ^(5)D_(4) state of the f–f inner-shell transition in the Tb system.However,under high-energy VUV excitation,the state switches into the ^(5)D_(3) state,which exhibits a blue emission.This mechanism is expected to be generally applicable to Tb-doped phosphors and useful in adjusting the optical properties against well-known cross-relaxation processes by varying the ratio of the green/blue contributions.