中国科大全球首次实现量子分解算法

日前，中国科大潘建伟教授领导的研究小组，在国际上首次实现了Shot量子分解算法，其研究成果发表在12月19日出版的美国权威物理学期刊《物理评论快报》上，这标志着我国光学量子计算研究达到了国际领先水平。

Theoretical Investigation on Photoionization and Dissociative Photoionization of Toluene

The photoionization and dissociation photoionization of toluene have been studied using quantum chemistry methods. The geometries and frequencies of the reactants, transition states and products have been performed at B3LYP/6-311＋＋G（d,p） level, and single-point energy calculations for all the stationary points were carried out at DFT calculations of the optimized structures with the G3B3 level. The ionization energies of toluene and the ap- pearance energies for major fragment ions, C7H7＋, C6H5＋, C5H6＋, C5H5＋, are determined to be 8.90, 11.15 or 11.03, 12.72, 13.69, 16.28 eV, respectively, which are all in good agree- ment with published experimental data. With the help of available published experimental data and theoretical results, four dissociative photoionization channels have been proposed： CTHT＋＋H, C6Hs＋＋CH3, C5H6＋WC2H2, CsHs＋＋C2H2＋H. Transition structures and intermediates for those isomerization processes are determined in this work. Especially, the structures of C5H6＋ and C5H5＋ produced by dissociative photoionization of toluene have been defined as chain structure in this work with theoretical calculations.

Structural and Infrared Spectroscopic Study on Solvation of Acetylene by Protonated Water Molecules

The effect of solvation on the conformation of acetylene has been studied by adding one water molecule at a time. Quantum chemical calculations of the n＋ （C2H2）（H2O）n （n=1-5） clusters indicate that the H2O molecules prefer to form the OH...Tr interaction rather than the CH...O interaction. This solvation motif is different from that of neutral （C2H2）（H2O）n （n=1-4） clusters, in which the H2O molecules prefer to form the CH...O and OH...C Hbonds. For the H＋（C2H2）（H2O）n cationic clusters, the first solvation shell consists of one ring structure with two OH...Tr H-bonds and three water molecules, which is completed at n=4. Simulated infrared spectra reveal that vibrational frequencies of OH... H-bonded O-H stretching afford a sensitive probe for exploring the solvation of acetylene by protonated water molecules. Infrared spectra of the H＋ （C2H2）（H2O）n （n=1-5） clusters could be readily measured by the infrared photodissociation technique and thus provide useful information for the understanding of solvation processes.

Infrared-Vacuum Ultraviolet Spectroscopic and Theoretical Study of Neutral Trimethylamine Dimer

Infrared-vacuum ultraviolet （IR-VUV） spectra of neutral trimethylamine dimer were mea- sured in the 2500-3800 cm-1 region. Quantum chemical calculations were performed to identify the structure of the low-lying isomers and to assign the observed spectral features. The bands at 2975 and 2949 cm-1 were assigned to the antisymmetric C-H stretching and the band at 2823 cm-1 to the symmetric C-H stretching, respectively. The 2739 cm-1 band was due to the CH3 bending overtone, which disappeared at low IR laser power of 1 mJ/mm2. The extra band at 2773 cm-1 could be due to Fermi resonance behavior of the light isotopologue, these are often close in energy and can strongly mix through cubic terms in the potential function. Experimental and theoretical results indicate the likely coexistence of multiple structures. The peak widths of IR spectra of neutral trimethylamine dimer are not significantly affected by the structural transformation, allowing the stretching modes to be well resolved.

Structural and Bonding Properties of Al_(n)C_(4)^(−/0)(n=2−4)Clusters:Anion Photoelectron Spectroscopy and Theoretical Calculations

We measured the photoelectron spectra of Al_(n)C_(4)^(−)(n=2−4)clusters by using size-selected anion photoelectron spectroscopy.The structures of Al_(n)C_(4)^(−/0)(n=2−4)clusters were explored with quantum chemistry calculations and were determined by comparing the theoretical results with the experimental spectra.It is found that the most stable structure of Al_(2)C_(4)^(−) anion is a C_(2v)symmetry planar structure with two Al atoms interacting with two C_(2)units.In addition,Al_(2)C_(4)^(−) anion also has a D∞h symmetry linear structure with two Al atoms located at the two ends of a C_(4)chain,which is slightly higher in energy than the planar structure.The most stable structure of neutral Al_(2)C_(4)has a D∞h symmetry linear structure.The most stable structure of Al_(3)C_(4)^(−) anion is a planar structure with three Al atoms interacting with two C_(2)units.Whereas neutral Al_(3)C_(4)cluster has a C_(2v)symmetric V-shaped bent structure.The global minima structures of both Al_(4)C_(4)^(−) and neutral Al_(4)C_(4)are C_(2)h symmetry planar structures with four Al atoms interacting with the ends of two C_(2)units.Adaptive natural density partitioning analyses of Al_(n)C_(4)^(−)(n=2−4)clusters show that the interactions between the Al atoms and C_(2)units have bothσandπcharacters.

Conformations and Structures of Ethoxycarbonyl Isothiocyanate Revealed by Rotational Spectroscopy

The ethoxycarbonyl isothiocyanate has been investigated by using supersonic jet Fourier transform microwave spectroscopy.Two sets of rotational spectra belonging to conformers TCC(with the backbone of C-C-O-C,C-O-C=O,and O-C(=O)-NCS being trans,cis,and cis arranged,respectively)and GCC(gauche,cis,and cis arrangement of the C-C-O-C,C-O-C=O,and O-C(=O)-NCS)have been measured and assigned.The measurements of13C,15N and34S mono-substituted species of the two conformers have also been performed.The comprehensive rotational spectroscopic investigations provide accurate values of rotational constants and14N quadrupole coupling constants,which lead to structural determinations of the two conformers of ethoxycarbonyl isothiocyanate.For conformer TCC,the values of Pcckeep constant upon isotopic substitution,indicating that the heavy atoms of TCC are effectively located in the ab plane.

Infrared Photodissociation Spectroscopic and Theoretical Study of [Co（CO2）n]+ Clusters

The mass-selected infrared photodissociation (IRPD) spectroscopy was utilized to investigate the interactions of cationic cobalt with carbon dioxide molecules. Quantum chemical calculations were performed on the [Co(CO2)n]^+ clusters to identify the structures of the low-lying isomers and to assign the observed spectral features. All the [Co(CO2)n]^+(n=2-6) clusters studied here show resonances near the CO2 asymmetric stretch of free CO2 molecule. Experimental and calculated results indicate that the CO2 molecules are weakly bound to the Co+ cations in an end-on con guration via a charge-quadrupole electrostatic interaction. The present IRPD spectra of [Co(CO2)n]^+ clusters have been compared to those of Ar-tagged species ([Co(CO2)n]^+-Ar), which would provide insights into the tagging effect of rare gas on the weakly-bounded clusters.

Infrared Spectroscopy of CO2 Transformation by Group Ⅲ Metal Monoxide Cations

Infrared photodissociation spectroscopy of mass-selected[MO(CO2)n]^+(M=Sc,Y,La)complexes indicates that the conversion from the solvated structure into carbonate one can be achieved by the ScO^+ cation at n=5 and by the YO^+ cation at n=4,while only the solvated structures are observed for the LaO^+ cation.These findings suggest that both the ScO^+ and YO^+cations are able to fix CO2 into carbonate.Quantum chemical calculations are performed on[MO(CO2)n]^+ to identify the structures of the low-lying isomers and to assign the observed spectral features.Theoretical analyses show that the[YO(CO2)n]^+ complex has the smallest barrier for the conversion from the solvated structure into carbonate one,while[LaO(CO2)n]^+ exhibits the largest conversion barrier among the three metal oxide cations.The present system affords a model in clarifying the effect of different metals in catalytic CO2 transformation at the molecular level.

Quantum-Chemical Interpretation of the Spectroscopy of Highly Luminescent 1,3,5-Triazapentadiene Complexes of Platinum（Ⅱ）

The quantum-chemical calculations were performed to determine the nature of the equilibrium geometry of the ground and excited states of the 1,3,5-triazapentadiene complexes of platinum（Ⅱ） and theirs nature and structure of molecular orbitals.

Testing a quantum error-correcting code on various platforms

Quantum error correction plays an important role in fault-tolerant quantum information processing.It is usually difficult to experimentally realize quantum error correction,as it requires multiple qubits and quantum gates with high fidelity.Here we propose a simple quantum error-correcting code for the detected amplitude damping channel.The code requires only two qubits.We implement the encoding,the channel,and the recovery on an optical platform,the IBM Q System,and a nuclear magnetic resonance system.For all of these systems,the error correction advantage appears when the damping rate exceeds some threshold.We compare the features of these quantum information processing systems used and demonstrate the advantage of quantum error correction on current quantum computing platforms.

Absorption Spectra and Refractive Index Changes of an Exciton in a Core/Shell Quantum Dot

The absorption spectra and the refractive index changes are calculated theoretically for an exeiton in a core/shell quantum dot. The advantage of our methodology is that one can investigate the influence of the repulsive core by varying two parameters in the confinement potential. The dimensionality effect of exciton quantum dots on the optical absorptions has been studied. It has been found that in the same regime, the optical absorption intensities of excitons axe much smaller for the core/shell quantum dots than for the two-dimensional quantum rings. The linear and the nonlinear optical absorption coefficients and refractive index changes have been examined with the change of the confinement potential. The results show that the optical absorptions and the refractive index changes are strongly affected by the repulsive core of core/shell quantum dots. Moreover, the calculated results also reveal that as the inner radius increases, the peak values of the absorption coefficients and the refractive index changes of an exciton will show the optical Aharonov-Bohm oscillation in core/shell quantum dots.