Kavli Institute of Nanoscience

About: Kavli Institute of Nanoscience is a based out in . It is known for research contribution in the topics: Quantum dot & Qubit. The organization has 292 authors who have published 248 publications receiving 11241 citations.

DNA Translocation through Graphene Nanopores

Abstract: Nanopores—nanosized holes that can transport ions and molecules—are very promising devices for genomic screening, in particular DNA sequencing. Solid-state nanopores currently suffer from the drawback, however, that the channel constituting the pore is long, ∼100 times the distance between two bases in a DNA molecule (0.5 nm for single-stranded DNA). This paper provides proof of concept that it is possible to realize and use ultrathin nanopores fabricated in graphene monolayers for single-molecule DNA translocation. The pores are obtained by placing a graphene flake over a microsize hole in a silicon nitride membrane and drilling a nanosize hole in the graphene using an electron beam. As individual DNA molecules translocate through the pore, characteristic temporary conductance changes are observed in the ionic current through the nanopore, setting the stage for future single-molecule genomic screening devices.

Direct force measurements on DNA in a solid-state nanopore

Abstract: Among the variety of roles for nanopores in biology, an important one is enabling polymer transport, for example in gene transfer between bacteria1 and transport of RNA through the nuclear membrane2. Recently, this has inspired the use of protein3,4,5 and solid-state6,7,8,9,10 nanopores as single-molecule sensors for the detection and structural analysis of DNA and RNA by voltage-driven translocation. The magnitude of the force involved is of fundamental importance in understanding and exploiting this translocation mechanism, yet so far it has remained unknown. Here, we demonstrate the first measurements of the force on a single DNA molecule in a solid-state nanopore by combining optical tweezers11 with ionic-current detection. The opposing force exerted by the optical tweezers can be used to slow down and even arrest the translocation of the DNA molecules. We obtain a value of 0.24±0.02 pN mV−1 for the force on a single DNA molecule, independent of salt concentration from 0.02 to 1 M KCl. This force corresponds to an effective charge of 0.50±0.05 electrons per base pair equivalent to a 75% reduction of the bare DNA charge.

Electrical control of a long-lived spin qubit in a Si/SiGe quantum dot.

Abstract: The electron spin in a silicon-based quantum dot can be controlled electrically for as long as several tens of microseconds, which improves the prospects for quantum information processing based on this type of quantum dot. Nanofabricated quantum bits permit large-scale integration but usually suffer from short coherence times due to interactions with their solid-state environment1. The outstanding challenge is to engineer the environment so that it minimally affects the qubit, but still allows qubit control and scalability. Here, we demonstrate a long-lived single-electron spin qubit in a Si/SiGe quantum dot with all-electrical two-axis control. The spin is driven by resonant microwave electric fields in a transverse magnetic field gradient from a local micromagnet2, and the spin state is read out in the single-shot mode3. Electron spin resonance occurs at two closely spaced frequencies, which we attribute to two valley states. Thanks to the weak hyperfine coupling in silicon, a Ramsey decay timescale of 1 μs is observed, almost two orders of magnitude longer than the intrinsic timescales in GaAs quantum dots4,5, whereas gate operation times are comparable to those reported in GaAs6,7,8. The spin echo decay time is ∼40 μs, both with one and four echo pulses, possibly limited by intervalley scattering. These advances strongly improve the prospects for quantum information processing based on quantum dots.

Identifying the mechanism of biosensing with carbon nanotube transistors

Abstract: Carbon nanotube transistors have outstanding potential for electronic detection of biomolecules in solution The physical mechanism underlying sensing however remains controversial, which hampers full exploitation of these promising nanosensors Previously suggested mechanisms are electrostatic gating, changes in gate coupling, carrier mobility changes, and Schottky barrier effects We argue that each mechanism has its characteristic effect on the liquid gate potential dependence of the device conductance By studying both the electron and hole conduction, the sensing mechanisms can be unambiguously identified From extensive protein-adsorption experiments on such devices, we find that electrostatic gating and Schottky barrier effects are the two relevant mechanisms, with electrostatic gating being most reproducible If the contact region is passivated, sensing is shown to be dominated by electrostatic gating, which demonstrates that the sensitive part of a nanotube transistor is not limited to the contact region, as previously suggested Such a layout provides a reliable platform for biosensing with nanotubes

Interfacing spin qubits in quantum dots and donors—hot, dense, and coherent

Abstract: Semiconductor spins are one of the few qubit realizations that remain a serious candidate for the implementation of large-scale quantum circuits. Excellent scalability is often argued for spin qubits defined by lithography and controlled via electrical signals, based on the success of conventional semiconductor integrated circuits. However, the wiring and interconnect requirements for quantum circuits are completely different from those for classical circuits, as individual direct current, pulsed and in some cases microwave control signals need to be routed from external sources to every qubit. This is further complicated by the requirement that these spin qubits currently operate at temperatures below 100 mK. Here, we review several strategies that are considered to address this crucial challenge in scaling quantum circuits based on electron spin qubits. Key assets of spin qubits include the potential to operate at 1 to 4 K, the high density of quantum dots or donors combined with possibilities to space them apart as needed, the extremely long-spin coherence times, and the rich options for integration with classical electronics based on the same technology.