01229nas a2200157 4500008004100000245007900041210006900120260001300189520074400202100001900946700001700965700001300982700002100995700001801016856003701034 2023 eng d00aEver more optimized simulations of fermionic systems on a quantum computer0 aEver more optimized simulations of fermionic systems on a quantu c3/6/20233 a

Despite using a novel model of computation, quantum computers break down programs into elementary gates. Among such gates, entangling gates are the most expensive. In the context of fermionic simulations, we develop a suite of compilation and optimization techniques that massively reduce the entangling-gate counts. We exploit the well-studied non-quantum optimization algorithms to achieve up to 24\% savings over the state of the art for several small-molecule simulations, with no loss of accuracy or hidden costs. Our methodologies straightforwardly generalize to wider classes of near-term simulations of the ground state of a fermionic system or real-time simulations probing dynamical properties of a fermionic system. 

1 aWang, Qingfeng1 aCian, Ze-Pei1 aLi, Ming1 aMarkov, Igor, L.1 aNam, Yunseong uhttps://arxiv.org/abs/2303.0346002193nas a2200157 4500008004100000245010400041210006900145260001400214490000600228520169000234100001901924700001301943700002401956700001801980856003701998 2021 eng d00aResource-Optimized Fermionic Local-Hamiltonian Simulation on Quantum Computer for Quantum Chemistry0 aResourceOptimized Fermionic LocalHamiltonian Simulation on Quant c7/21/20210 v53 a

The ability to simulate a fermionic system on a quantum computer is expected to revolutionize chemical engineering, materials design, nuclear physics, to name a few. Thus, optimizing the simulation circuits is of significance in harnessing the power of quantum computers. Here, we address this problem in two aspects. In the fault-tolerant regime, we optimize the $\rzgate$ and $\tgate$ gate counts along with the ancilla qubit counts required, assuming the use of a product-formula algorithm for implementation. We obtain a savings ratio of two in the gate counts and a savings ratio of eleven in the number of ancilla qubits required over the state of the art. In the pre-fault tolerant regime, we optimize the two-qubit gate counts, assuming the use of the variational quantum eigensolver (VQE) approach. Specific to the latter, we present a framework that enables bootstrapping the VQE progression towards the convergence of the ground-state energy of the fermionic system. This framework, based on perturbation theory, is capable of improving the energy estimate at each cycle of the VQE progression, by about a factor of three closer to the known ground-state energy compared to the standard VQE approach in the test-bed, classically-accessible system of the water molecule. The improved energy estimate in turn results in a commensurate level of savings of quantum resources, such as the number of qubits and quantum gates, required to be within a pre-specified tolerance from the known ground-state energy. We also explore a suite of generalized transformations of fermion to qubit operators and show that resource-requirement savings of up to more than 20% is possible.

1 aWang, Qingfeng1 aLi, Ming1 aMonroe, Christopher1 aNam, Yunseong uhttps://arxiv.org/abs/2004.0415101739nas a2200205 4500008004100000245013400041210006900175260001500244520106400259100001801323700001201341700002201353700001701375700002501392700001301417700001901430700002601449700002101475856003701496 2019 eng d00aFeshbach resonances in p-wave three-body recombination within Fermi-Fermi mixtures of open-shell 6Li and closed-shell 173Yb atoms0 aFeshbach resonances in pwave threebody recombination within Ferm c12/10/20193 a

We report on observations and modeling of interspecies magnetic Feshbach resonances in dilute ultracold mixtures of open-shell alkali-metal 6Li and closed-shell 173Yb atoms with temperatures just above quantum degeneracy for both fermionic species. Resonances are located by detecting magnetic-field-dependent atom loss due to three-body recombination. We resolve closely-located resonances that originate from a weak separation-dependent hyperfine coupling between the electronic spin of 6Li and the nuclear spin of 173Yb, and confirm their magnetic field spacing by ab initio electronic-structure calculations. Through quantitative comparisons of theoretical atom-loss profiles and experimental data at various temperatures between 1 μK and 20 μK, we show that three-body recombination in fermionic mixtures has a p-wave Wigner threshold behavior leading to characteristic asymmetric loss profiles. Such resonances can be applied towards the formation of ultracold doublet ground-state molecules and quantum simulation of superfluid p-wave pairing.

1 aGreen, Alaina1 aLi, Hui1 aToh, Jun, Hui See1 aTang, Xinxin1 aMcCormick, Katherine1 aLi, Ming1 aTiesinga, Eite1 aKotochigova, Svetlana1 aGupta, Subhadeep uhttps://arxiv.org/abs/1912.0487401691nas a2200169 4500008004100000245007000041210006900111260001500180300001300195490000600208520118500214100002701399700001301426700001901439700002601458856003701484 2018 eng d00aFractal Universality in Near-Threshold Magnetic Lanthanide Dimers0 aFractal Universality in NearThreshold Magnetic Lanthanide Dimers c2018/02/16 aeaap83080 v43 a

Ergodic quantum systems are often quite alike, whereas nonergodic, fractal systems are unique and display characteristic properties. We explore one of these fractal systems, weakly bound dysprosium lanthanide molecules, in an external magnetic field. As recently shown, colliding ultracold magnetic dysprosium atoms display a soft chaotic behavior with a small degree of disorder. We broaden this classification by investigating the generalized inverse participation ratio and fractal dimensions for large sets of molecular wave functions. Our exact close-coupling simulations reveal a dynamic phase transition from partially localized states to totally delocalized states and universality in its distribution by increasing the magnetic field strength to only a hundred Gauss (or 10 mT). Finally, we prove the existence of nonergodic delocalized phase in the system and explain the violation of ergodicity by strong coupling between near-threshold molecular states and the nearby continuum.

1 aMakrides, Constantinos1 aLi, Ming1 aTiesinga, Eite1 aKotochigova, Svetlana uhttps://arxiv.org/abs/1802.0958601661nas a2200121 4500008004100000245009700041210006900138520123700207100001301444700001901457700002601476856003701502 2018 eng d00aOrbital quantum magnetism in spin dynamics of strongly interacting magnetic lanthanide atoms0 aOrbital quantum magnetism in spin dynamics of strongly interacti3 a

Laser cooled lanthanide atoms are ideal candidates with which to study strong and unconventional quantum magnetism with exotic phases. Here, we use state-of-the-art closed-coupling simulations to model quantum magnetism for pairs of ultracold spin-6 erbium lanthanide atoms placed in a deep optical lattice. In contrast to the widely used single-channel Hubbard model description of atoms and molecules in an optical lattice, we focus on the single-site multi-channel spin evolution due to spin-dependent contact, anisotropic van der Waals, and dipolar forces. This has allowed us to identify the leading mechanism, orbital anisotropy, that governs molecular spin dynamics among erbium atoms. The large magnetic moment and combined orbital angular momentum of the 4f-shell electrons are responsible for these strong anisotropic interactions and unconventional quantum magnetism. Multi-channel simulations of magnetic Cr atoms under similar trapping conditions show that their spin-evolution is controlled by spin-dependent contact interactions that are distinct in nature from the orbital anisotropy in Er. The role of an external magnetic field and the aspect ratio of the lattice site on spin dynamics is also investigated.

1 aLi, Ming1 aTiesinga, Eite1 aKotochigova, Svetlana uhttps://arxiv.org/abs/1804.1010217147nas a2200181 45000080041000002450100000412100069001412600015002103000011002254900007002365201657700243100001316820700002216833700002716855700001916882700002716901856003716928 2017 eng d00aPendular trapping conditions for ultracold polar molecules enforced by external electric fields0 aPendular trapping conditions for ultracold polar molecules enfor c2017/06/26 a0634220 v953 a

We theoretically investigate trapping conditions for ultracold polar molecules in optical lattices, when external magnetic and electric fields are simultaneously applied. Our results are based on an accurate electronic-structure calculation of the polar 23Na40K polar molecule in its absolute ground state combined with a calculation of its rovibrational-hyperfine motion. We find that an electric field strength of 5.26(15) kV/cm and an angle of 54.7 between this field and the polarization of the optical laser lead to a trapping design for 23Na40K molecules where decoherences due laser-intensity fluctuations and fluctuations in the direction of its polarization are kept to a minimum. One standard deviation systematic and statistical uncertainties are given in parenthesis. Under such conditions pairs of hyperfine-rotational states of v=0 molecules, used to induce tunable dipole-dipole interactions between them, experience ultrastable, matching trapping forces.

1 aLi, Ming1 aPetrov, Alexander1 aMakrides, Constantinos1 aTiesinga, Eite1 aKotochigova, Svetlanta uhttps://arxiv.org/abs/1703.03839