Development of wave-packet interference control with an attosecond accuracy and is application to quantum computing

波函数的量子位相操纵开启了一项新技术，它通过量子计算和键选择化学等“相干控制”来实现。一种有希望的方法是使用相干光来调制波函数的光学相位。例如，用带宽足以覆盖几个振动本征态的飞秒(Fs)光脉冲照射一个双原子分子，相干地叠加这些本征态，产生一个空间局域波函数，称为核波包(WP)，沿着键轴来回传播。在这个WP的一般情况下，光场的相位被压印在WP上作为它的量子相位。因此，以比光周期更高的精度设计光学位相可以使我们以同样的精度设计WP的位相。我们研制了阿秒位相调制器，利用它我们可以以7阿秒的精度操纵两个飞秒激光脉冲的相对位相。这对飞秒激光脉冲被用来实现两个核WP在单个汞-Ar分子中运动的前所未有的高分辨率干涉，其条纹对比度几乎为100%，显示出重粒子的纯波性质。这种高分辨率的WP干涉已被用来将9个典型的三进制代码编码成一个组装在单个分子中的3个三值量子调节器作为WP的节点图。原则上，它可用于存储包含在光场中的位相信息。此外，利用这种WP干涉控制，我们发展了一个高精度的移相器，它工作在由单个分子内两个或三个振动本征态的相干叠加组成的量子轨道上。目前的研究表明，使用单个分子中的多个振动本征态进行大规模量子计算是可能的。

Quantum phase manipulation of wave functions opens a novel technology through "coherent control" such as quantum computing and bond selective chemistry. One promising approach is to use coherent light to modulate a wave function with its optical phase. For example, irradiating a diatomic molecule with a femtosecond (fs) optical pulse, with bandwidth broad enough to cover several vibrational eigenstates, coherently superpose those eigenstates to yield a spatially localized wave function called a nuclear "wave packet (WP)" traveling back and forth along the bond axis. In the generalon of this WP, the phase of an optical field is imprinted on the WP as its quantum phase. Hence engineering the optical phase with an accuracy better than the optical cycle allows us to engineer the phase of the WP with the same accuracy.We have developed the "attosecond phase modulator", by which we can manipulate the relative phase of two fs laser pulses with an accuracy of 7 attoseconds. This phased pair of fs laser pulses has been used to realize unprecedented high-resolution interference of two nuclear WP's moving in a single Hg-Ar molecule where its fringe contrast is almost 100 %, demonstrating a pure wave nature of heavy particles.This high-resolution WP interference has been utilized to encode 9 typical trinary codes into a 3 tritquantum reglster assembled within a single molecule as nodal patterns of a WP. In principle it can be used for fhe storage of the phase information contained in an optical field. Moreover, by using this WP interference control, we have developed a high-precision phase shiffer operated on a qubitorqutrit composed of coherent superposition of two or three vibrational eigenstates within a single molecule. The present studies indicate a possibility of large-sale quantum computing using many vibrational eigenstates within a single molecule.