Preliminary Frequency Comparison of Two 40^Ca^＋ Optical Frequency Standards

Frequency comparison is one of the most efficient ways to evaluate the performance of a frequency standard. Based on the pre-existing 40^Ca＋ optical frequency standard, we set up the second 40^Ca^＋ optical frequency standard, which has been improved in the materials and structure of ion traps for better control of the magnetic field. After the compensation, the residual magnetic field at the position of the ion is adjusted to be～500nT with a long time jitter of～10nT, which is better than the pre-existing 40^Ca^＋ optical frequency standard. We realize the ＇4-point-closed-loop locking＇ on the second 40^Ca＋ optical frequency standard after a series of preparatory works. Through half an hour of measurement time, the two frequency standards exhibited a stability of 2.1 × 10^-13.τ^1/2 and a relative frequency difference of 1.5 （2.9）Hz.     

Microwave-Optical Double-Resonance Spectroscopy Experiment of 199Hg＋ Ground State Hyperfine Splitting in a Linear Ion Trap

We report a spectroscopy experiment of the ^199Hg＋ ions are optically pumped by a discharge lamp and splitting is measured to be 40507347996.8（0.1）Hz by line width as 30mHz is also observed. This progress ion frequency standards. ground state hyperfine splitting in a linear ion trap. The cooled by helium buffer gas. The ground state hyperfine the mierowave-optical double-resonance method. A nsrrow builds the foundation for the realization of trapped ^199Hg＋     

The influence of Exciting Frequency on N2 and N2+ Vibrational Temperature of Nitrogen Capacitively Coupled Plasma

By using optical emission spectroscopy （OES）, N2 and N2^＋ vibrational temperatures in capacitively coupled plasma discharges with different exciting frequencies are investigated. The vibrational temperatures are acquired by comparing the measured and calculated spectra of selected transitions with a least-square procedure. It is found that N2 and N2^＋ vibrational temperatures almost increase linearly with increasing exciting frequency up to 23 MHz, then increase slowly or even decrease. The pressure corresponding to the maximum point of N2 vibrational temperature decreases with the increasing exciting frequency. These experimental phenomena are attributed to the increasing electron density, whereas the electron temperature decreases with exciting frequency rising.     

Experimental Improvement of Signal of a Single Laser-Cooled Trapped ^40Ca^＋ Ion

A single ^40Ca^＋ ion is loaded in a miniature Paul trap and the probability of directly loading a single ion is above 50%. The signal-to-noise ratio and the storage time for a single ion have been improved by minimizing the ion micromotion and locking a 397nm cooling laser to a Fabry-Perot interferometer and optogalvanic signal. From the fluorescence spectrum, the ion temperature is estimated to be about 5mK.     

Frequency-Shift of a Frequency Stabilized Laser Based on Zeeman Effect

We introduce a new method of frequency-shifting for a diode laser in laser cooling experiments, the method is based on the Zeeman egect of^87 Rb atoms. The laser frequency is stabilized by absorption spectrum line of atoms in magnetic field. We show that a magnetic field can be added up to 10^-2T. The corresponding frequency shift is 10^2 MHz and the response time is about 1ms. The large range of the frequency shift is suffcient for laser-cooling experiments.     

Branching Ratios of α Decay for Nuclei near Deformed Shell Closures

The generalized liquid drop model （GLDM） is extended to the region around deformed shell closure ^270Hs by taking into account the excitation energy EI＋ of the residual daughter nucleus and the centrifugal potential energy Vcen（r）. The branching ratios of a decays from the ground state of a parent nucleus to the ground state 0^＋ of its deformed daughter nucleus and to the first excited state 2^＋ are calculated in the framework of the GLDM. The results support the proposal that a measurement of a spectroscopy is a feasible method to extract information on nuclear deformation of superheavy nuclei around the deformed nucleus ^270Hs.     

Investigation of analytical harmonic frequency and potential energy function,vibrational levels for the X^2∑^＋ and A^2Л states of CN radical

This paper calculates the equilibrium structure and the potential energy functions of the ground state （X^2∑^＋） and the low lying excited electronic state （A^2Л） of CN radical are calculated by using CASSCF method. The potential energy curves are obtained by a least square fitting to the modified Murrell-Sorbie function. On the basis of physical theory of potential energy function, harmonic frequency （ωe） and other spectroscopic constants （ωeχe, βe and αe） are calculated by employing the Rydberg-Klei-Rees method. The theoretical calculation results are in excellent agreement with the experimental and other complicated theoretical calculation data. In addition, the eigenvalues of vibrational levels have been calculated by solving the radial one-dimensional SchrSdinger equation of nuclear motion using the algebraic method based on the analytical potential energy function.     

Planar ion chip design for scalable quantum information processing

We investigate a planar ion chip design with a two-dimensional array of linear ion traps for scalable quantum information processing. Qubits are formed from the internal electronic states of trapped ^40Ca^＋ ions. The segmented electrodes reside in a single plane on a substrate and a grounded metal plate separately, a combination of appropriate rf and DC potentials is applied to them for stable ion confinement. Every two adjacent electrodes can generate a linear ion trap in and between the electrodes above the chip at a distance dependent on the geometrical scale and other considerations. The potential distributions are calculated by using a static electric field qualitatively. This architecture provides a conceptually simple avenue to achieving the microfabrication and large-scale quantum computation based on the arrays of trapped ions.     

Microwave Atomic Clock in the Optical Lattice with Specific Frequency

A scheme for a microwave atomic clock is proposed for Cs or Rb atoms trapped in a blue detuned optical lattice. The ac Stark shift of the clock transition due to a trapping laser is calculated. We analyze it at some specific laser wavelength. Compared with the case of the fountain clock, the cavity related shifts, the collision shift and the Doppler effect are eliminated or suppressed dramatically in an atomic lattice clock. By analyzing various sources of clock uncertainty, a microwave atomic lattice clock with a high accuracy and small volume is feasible.     

Observation of Spin Polarized Clock Transition in 87Sr Optical Lattice Clock

Atomic clocks operating at optical frequencies, with much better accuracy compared with microwave atomic clocks, have been assumed to be the next- generation time and frequency standards, Many applications will benefit from this lower frequency un- certainty of optical clocks, such as the re-definition of ＇the second＇, i.e. one of the seven base units of the international system of units （SI）, test of the time variation of fundamental physical constants and rel- ativity geodesy. Recently, the neutral atom lattice clock has achieved a lower frequency uncertainty com- pared with the optical ion clock, mainly due to the im- provement of the clock laser frequency stability refer- enced to a long high-finesse ULE cavity and the more accurate evaluation of black-body radiation shift. Strontium is an excellent candidate for the neutral atom optical clock. For the fermionic isotope of stron- tium, it has intrinsically less collision shift and the first order Zeeman shift can be removed by an inter- leaved probing approach.Recently, through the pre-cise measurement of the polarizability of strontium, the black body radiation （BBR） shift of the stron- tium lattice clock, which remains to be the limitation factor of its total frequency uncertainty, is reduced to a lower 10^-18 value.The instability of the strontium lattice clock has reached 3.1 × 10-16/√T, showing the significant advantage over the single ion optical clock. The total systematic uncertainty has reached 6.4 × 10^-18 in fractional frequency, which is the best among all optical clocks until now.     

Properties of Linear Entropy in k-Photon Jaynes-Cummings Model with Stark Shift and Kerr-Like Medium

The time evolution of the linear entropy of an taking into consideration Stark shift and Kerr-like medium. atom in k-photon daynes-Cummings model is investigated The effect of both the Stark shift and Kerr-like medium on the linear entropy is analyzed using a numerical technique for the field initially in coherent state and in even coherent state. The results show that the presence of the Kerr-like medium and Stark shift has an important effect on the properties of the entropy and entanglement. It is also shown that the setting of the initial state plays a significant role in the evolution of the linear entropy and entanglement.     

Carrier suppression in quadruple frequency modulation by cascaded optical external modulators for millimeter-wave generation

The optical carrier suppression in optical quadruple frequency modulation by cascaded external modulators is investigated theoretically and experimentally. Theoretical analysis demonstrates that the optical carrier suppression ratio is related with not only the initial phase difference of electrical signals applied on the two modulators, but also the optical phase shift between the two modulators. The maximum suppression ratio can be achieved when the total phase difference is equal to nπ＋π/2 （n = 1, 2,…）, which is verified by experiments. By properly controlling the total phase shift, 40-GHz millimeter-wave is generated by using a 10-GHz radio frequency （RF） source and the modulators.     

Precision spectroscopy with a single ~(40)Ca~+ ion in a Paul trap

Precision measurement of the 4s2S1/2–3d2D5/2clock transition based on40Ca+ion at 729 nm is reported. A single40Ca+ion is trapped and laser-cooled in a ring Paul trap, and the storage time for the ion is more than one month. The linewidth of a 729 nm laser is reduced to about 1 Hz by locking to a super cavity for longer than one month uninterruptedly.The overall systematic uncertainty of the clock transition is evaluated to be better than 6.5×10-16. The absolute frequency of the clock transition is measured at the 10-15 level by using an optical frequency comb referenced to a hydrogen maser which is calibrated to the SI second through the global positioning system(GPS). The frequency value is 411 042 129776 393.0(1.6) Hz with the correction of the systematic shifts. In order to carry out the comparison of two40Ca+optical frequency standards, another similar40Ca+optical frequency standard is constructed. Two optical frequency standards exhibit stabilities of 1×10-14τ-1/2with 3 days of averaging. Moreover, two additional precision measurements based on the single trapped40Ca+ion are carried out. One is the 3d2D5/2state lifetime measurement, and our result of 1174(10) ms agrees well with the results reported in [Phys. Rev. A 62 032503(2000)] and [Phys. Rev. A 71 032504(2005)]. The other one is magic wavelengths for the 4s2S1/2–3d2D5/2clock transition; λ|m j|=1/2= 395.7992(7) nm and λ|m j|=3/2=395.7990(7) nm are reported, and it is the first time that two magic wavelengths for the40Ca+clock-transition have been reported.     

Control of entanglement between two atoms by the Stark shift

Considering a quantum model consisting of two effective two-level atoms and a single-mode cavity,this paper investigates the entanglement dynamics between the two atoms,and studies the effect of the Stark shift on the entanglement.The results show that,on the one hand the atom-atom entanglement evolves periodically with time and the periods are affected by the Stark shift;on the other hand,the two atoms are not disentangled at any time when the Stark shift is considered,and for large values of the Stark shift parameter,the two atoms can remain in a stationary entangled state.In addition,for the initially partially entangled atomic state,the atom-atom entanglement can be greatly enhanced due to the presence of Stark shift.These properties show that the Stark shift can be used to control entanglement between two atoms.     

Ab initio calculations on the spectroscopic constants, vibrational levels and classical turning points for the 21∏u state of dimer 7Li2

The accurate dissociation energy and harmonic frequency for the highly excited 2^1Пu state of dimer ^7Li2 have been calculated using a symmetry-adapted-cluster configuration-interaction method in complete active space. The calculated results are in excellent agreement with experimental measurements. The potential energy curves at numerous basis sets for this state are obtained over a wide internuclear separation range from about 2.4a0 to 37.0a0. And the conclusion is gained that the basis set 6-311＋＋G（d,p） is a most suitable one. The calculated spectroscopic constants De, Re, ωe, ωeχe, ae and Be at 6-311＋＋G（d,p） are 0.9670 eV, 0.3125 nm, 238.6 cm^-1, 1.3705 cm^-1, 0.0039 cm^-1 and 0.4921 cm^-1, respectively. The vibrational levels are calculated by solving the radial SchrSdinger equation of nuclear motion. A total of 53 vibrational levels are found and reported for the first time. The classical turning points have been computed. Comparing with the measurements, in which only the first nine vibrational levels have been obtained so far, the present calculations are very encouraging. A careful comparison of the present results of the parameters De and We with those obtained from previous theories clearly shows that the present calculations are much closer to the measurements than previous theoretical results, thus representing an improvement on the accuracy of the ab initio calculations of the potentials for this state.     

Stabilization and Shift of Frequency in an External Cavity Diode Laser with Solenoid-Assisted Saturated Absorption

A simple method to realize both stabilization and shift of the frequency in an external cavity diode laser （ECDL） is reported. Due to the Zeeman effect, the saturated absorption spectrum of Rb atoms in a magnetic field is shifted. This shift can be used to detune the frequency of the ECDL, which is locked to the saturated absorption spectrum. The frequency shift amount can be controlled by changing the magnetic field for a specific polarization state of the laser beam. The advantages of this tunable frequency lock include low laser power requirement, without additional power loss, cheapness, and so on.     

Scheme for teleportation of unknown states of trapped ion

A scheme is presented for teleporting an unknown state in a trapped ion system. The scheme only requires a single laser beam. It allows the trap to be in any state with a few phonons, e.g. a thermal motion. Furthermore, it works in the regime, where the Rabi frequency of the laser is on the order of the trap frequency. Thus, the teleportation speed is greatly increased, which is important for decreasing the decoherence effect. This idea can also be used to teleport an unknown ionic entangled state.     

Direct Laser Cooling Al~+ Ion Optical Clocks

The Al~+ ion optical clock is a very promising optical frequency standard candidate due to its extremely small black-body radiation shift. It has been successfully demonstrated with the indirect cooled, quantum-logic-based spectroscopy technique. Its accuracy is limited by second-order Doppler shift, and its stability is limited by the number of ions that can be probed in quantum logic processing. We propose a direct laser cooling scheme of Al~+ ion optical clocks where both the stability and accuracy of the clocks are greatly improved. In the proposed scheme,two Al~+ traps are utilized. The first trap is used to trap a large number of Al~+ ions to improve the stability of the clock laser,while the second trap is used to trap a single Al~+ ion to provide the ultimate accuracy. Both traps are cooled with a continuous wave 167 nm laser. The expected clock laser stability can reach9.0×10~(-17)/τ~(1/2). For the second trap, in addition to 167 nm laser Doppler cooling, a second stage pulsed 234 nm two-photon cooling laser is utilized to further improve the accuracy of the clock laser. The total systematic uncertainty can be reduced to about 1×10~(-18). The proposed Al~+ ion optical clock has the potential to become the most accurate and stable optical clock.     

Ion source effect on the bond length of ^4HeH^＋

The bond length of ^4HeH^＋ resulting from collision-induced destruction is measured at 1.4420 MeV using the Coulomb Explosion Technique. The measured bond length of ^4HeH^＋ is 0.094±0.003nm. The bond length of ^4HeH^＋ obtained with our radio frequency （RF） ion source is larger than that obtained with a duoplasmatron ion source at Argonne National Laboratory （ANL）, but the bond lengths of H^＋2 and H^＋3obtained separately by ANL and by us with the two different ion sources are consistent with each other, which implies that there exists an ion source effect on the bond length of ^4HeH^＋. The main reason why the 4^4HeH^＋ bond lengths obtained by the two different ion sources are different is also discussed.