Hydrogen as a Source of Flux Noise in SQUIDs

Superconducting qubits are hampered by flux noise produced by surface spins from a variety of microscopic sources. Recent experiments indicated that hydrogen (H) atoms may be one of those sources. Using density functional theory calculations, we report that H atoms either embedded in, or adsorbed on, an a-Al2O3(0001) surface have sizeable spin moments ranging from 0.81 to 0.87 uB with energy barriers for spin reorientation as low as ~10 mK. Furthermore, H adatoms on the surface attract gas molecules such as O2, producing new spin sources. We propose coating the surface with graphene to eliminate H-induced surface spins and to protect the surface from other adsorbates.Comment: 12 pages, 4 figure

Disentanglement in a quantum critical environment

We study the dynamical process of disentanglement of two qubits and two qutrits coupled to an Ising spin chain in a transverse field, which exhibits a quantum phase transition. We use the concurrence and negativity to quantify entanglement of two qubits and two qutrits, respectively. Explicit connections between the concurrence (negativity) and the decoherence factors are given for two initial states, the pure maximally entangled state and the mixed Werner state. We find that the concurrence and negativity decay exponentially with fourth power of time in the vicinity of critical point of the environmental system.Comment: 8 pages, 6 figure

Alkyl-Alkyl Suzuki Cross-Coupling of Unactivated Secondary Alkyl Chlorides

No such thing as a problem substrate! In a reaction designed specifically for the title substrates C-C coupling with alkyl boranes occurred in good yield at room temperature with commercially available catalyst components (see scheme). This versatile method is also suitable for Suzuki reactions of secondary and primary alkyl bromides and iodides, as well as primary alkyl chlorides.National Institute of General Medical Sciences (U.S.) (Grant R01-GM62871)Eli Lilly and Company (Fellowship)Martin Family Society of Fellows for Sustainability (Fellowship)Merck Research LaboratoriesNovartis (Firm

Alkyl-Alkyl Suzuki Cross-Coupling of Unactivated Secondary Alkyl Chlorides

No such thing as a problem substrate! In a reaction designed specifically for the title substrates C-C coupling with alkyl boranes occurred in good yield at room temperature with commercially available catalyst components (see scheme). This versatile method is also suitable for Suzuki reactions of secondary and primary alkyl bromides and iodides, as well as primary alkyl chlorides

Tropical Fock-Goncharov coordinates for SL3\mathrm{SL}_3-webs on surfaces II: naturality

In a companion paper (arXiv 2011.01768) we constructed non-negative integer coordinates $\Phi_\mathcal{T}$ for a distinguished collection $\mathcal{W}_{3, \widehat{S}}$ of $\mathrm{SL}_3$-webs on a finite-type punctured surface $\widehat{S}$, depending on an ideal triangulation $\mathcal{T}$ of $\widehat{S}$. We prove that these coordinates are natural with respect to the choice of triangulation, in the sense that if a different triangulation $\mathcal{T}^\prime$ is chosen then the coordinate change map relating $\Phi_\mathcal{T}$ and $\Phi_{\mathcal{T}^\prime}$ is a prescribed tropical cluster transformation. Moreover, when $\widehat{S}=\Box$ is an ideal square, we provide a topological geometric description of the Hilbert basis (in the sense of linear programming) of the non-negative integer cone $\Phi_\mathcal{T}(\mathcal{W}_{3, \Box}) \subset \mathbb{Z}_{\geq 0}^{12}$, and we prove that this cone canonically decomposes into 42 sectors corresponding topologically to 42 families of $\mathrm{SL}_3$-webs in the square.Comment: 39 pages, 27 figure