Read-out of superconducting single photon detectors

Detection arrangement having an array of at least one superconducting single photon detector (SSPD). The detection arrangement further has a cryogenic part (9) with the array of at least one SSPD (1), the cryogenic part (9) being at a superconducting temperature in operation. Also, a separate charge storage element (5) in the form of an electronic component, is provided which is connected to an output terminal (3) of each of the at least one SSPD (1). The separate charge storage elements (5) are positioned on the cryogenic part (9).QN/Quantum NanoscienceApplied Science

Capacitive readout and gating of superconducting single photon detectors

We propose and develop a readout scheme for superconducting single-photon detectors based on an integrated circuit, relaxing the need for large bandwidth amplification and resulting in voltage steps proportional to the number of detected photons. We also demonstrate time gating, to filter scattered light in time and reduce dark counts. This could lead to a higher signal-to-noise ratio. The gate pulse is generated on the detection of a photon created by a spontaneous parametric down-conversion source, heralding the presence of a second photon. These two schemes could find applications within advanced multi-array imaging detection systems.QN/Quantum NanoscienceApplied Science

Probing DNA Translocations with Inplane Current Signals in a Graphene Nanoribbon with a Nanopore

Many theoretical studies predict that DNA sequencing should be feasible by monitoring the transverse current through a graphene nanoribbon while a DNA molecule translocates through a nanopore in that ribbon. Such a readout would benefit from the special transport properties of graphene, provide ultimate spatial resolution because of the single-atom layer thickness of graphene, and facilitate high-bandwidth measurements. Previous experimental attempts to measure such transverse inplane signals were however dominated by a trivial capacitive response. Here, we explore the feasibility of the approach using a custom-made differential current amplifier that discriminates between the capacitive current signal and the resistive response in the graphene. We fabricate well-defined short and narrow (30 nm × 30 nm) nanoribbons with a 5 nm nanopore in graphene with a high-temperature scanning transmission electron microscope to retain the crystallinity and sensitivity of the graphene. We show that, indeed, resistive modulations can be observed in the graphene current due to DNA translocation through the nanopore, thus demonstrating that DNA sensing with inplane currents in graphene nanostructures is possible. The approach is however exceedingly challenging due to low yields in device fabrication connected to the complex multistep device layout.BN/Cees Dekker LabQN/Zandbergen LabGenera

Deterministic delivery of remote entanglement on a quantum network

Large-scale quantum networks promise to enable secure communication, distributed quantum computing, enhanced sensing and fundamental tests of quantum mechanics through the distribution of entanglement across nodes 1-7. Moving beyond current two-node networks 8-13 requires the rate of entanglement generation between nodes to exceed the decoherence (loss) rate of the entanglement. If this criterion is met, intrinsically probabilistic entangling protocols can be used to provide deterministic remote entanglement at pre-specified times. Here we demonstrate this using diamond spin qubit nodes separated by two metres. We realize a fully heralded single-photon entanglement protocol that achieves entangling rates of up to 39 hertz, three orders of magnitude higher than previously demonstrated two-photon protocols on this platform 14. At the same time, we suppress the decoherence rate of remote-entangled states to five hertz through dynamical decoupling. By combining these results with efficient charge-state control and mitigation of spectral diffusion, we deterministically deliver a fresh remote state with an average entanglement fidelity of more than 0.5 at every clock cycle of about 100 milliseconds without any pre-or post-selection. These results demonstrate a key building block for extended quantum networks and open the door to entanglement distribution across multiple remote nodes.Accepted Author Manuscript Change history: In this Letter, the received date should be 20 December 2017, instead of 27 April 2018. This has been corrected online. De daarbij behorende doi 10.1038/s41586-018-0314-9QID/Hanson LabGeneralQN/Hanson La

Low-frequency noise in Josephson junctions for superconducting qubits

The authors have studied low-frequency resistance fluctuations in shadow-evaporated Al/AlOx/Al tunnel junctions. Between 300 and 5?K the spectral density follows a 1/f law. Below 5?K, individual defects distort the 1/f shape of the spectrum. The spectral density decreases linearly with temperature between 150 and 1?K and saturates below 0.8?K. At 4.2?K, it is about two orders of magnitude lower than expected from a recent survey [D. J. Van Harlingen et al., Phys. Rev. B 70, 064510 (2004)]. Due to saturation below 0.8?K the estimated qubit dephasing times at 100?mK are only about two times longer than calculated by Van Harlingen et al.Kavli Institute of NanoscienceApplied Science

Impact of Classical Control Electronics on Qubit Fidelity

Quantum processors rely on classical electronic controllers to manipulate and read out the state of quantum bits (qubits). As the performance of the quantum processor improves, nonidealities in the classical controller can become the performance bottleneck for the whole quantum computer. To prevent such limitation, this paper presents a systematic study of the impact of the classical electrical signals on the qubit fidelity. All operations, i.e., single-qubit rotations, two-qubit gates, and readout, are considered, in the presence of errors in the control electronics, such as static, dynamic, systematic, and random errors. Although the presented study could be extended to any qubit technology, it currently focuses on single-electron spin qubits, because of several advantages, such as purely electrical control and long coherence times, and for their potential for large-scale integration. As a result of this study, detailed electrical specifications for the classical control electronics for a given qubit fidelity can be derived. We also discuss how qubit fidelity is affected by the limited performance of the general-purpose room-temperature equipment typically employed to control the few qubits available today. Ultimately, we show that tailor-made electronic controllers can achieve significantly lower power, cost, and size, as required to support the scaling up of quantum computers.OLD QCD/Charbon LabQuTechGeneralQCD/Veldhorst LabQCD/Vandersypen LabQN/Vandersypen LabElectronics(OLD)Applied Quantum Architecture

A capacitance spectroscopy-based platform for realizing gate-defined electronic lattices

Electrostatic confinement in semiconductors provides a flexible platform for the emulation of interacting electrons in a two-dimensional lattice, including in the presence of gauge fields. This combination offers the potential to realize a wide host of quantum phases. Capacitance spectroscopy provides a technique that allows one to directly probe the density of states of such two-dimensional electron systems. Here, we present a measurement and fabrication scheme that builds on capacitance spectroscopy and allows for the independent control of density and periodic potential strength imposed on a two-dimensional electron gas. We characterize disorder levels and (in)homogeneity and develop and optimize different gating strategies at length scales where interactions are expected to be strong. A continuation of these ideas might see to fruition the emulation of interaction-driven Mott transitions or Hofstadter butterfly physics.Vandersypen LabQN/Quantum TransportGeneralQN/Vandersypen La

Realization of a multinode quantum network of remote solid-state qubits

The distribution of entangled states across the nodes of a future quantum internet will unlock fundamentally new technologies. Here, we report on the realization of a three-node entanglement-based quantum network. We combine remote quantum nodes based on diamond communication qubits into a scalable phase-stabilized architecture, supplemented with a robust memory qubit and local quantum logic. In addition, we achieve real-time communication and feed-forward gate operations across the network. We demonstrate two quantum network protocols without postselection: the distribution of genuine multipartite entangled states across the three nodes and entanglement swapping through an intermediary node. Our work establishes a key platform for exploring, testing, and developing multinode quantum network protocols and a quantum network control stack.Accepted Author ManuscriptQuTechQID/Hanson LabGeneralBUS/Quantum DelftQID/Wehner GroupQuantum Internet DivisionQuantum Information and SoftwareQN/Hanson La

Spin Lifetime and Charge Noise in Hot Silicon Quantum Dot Qubits

We investigate the magnetic field and temperature dependence of the single-electron spin lifetime in silicon quantum dots and find a lifetime of 2.8 ms at a temperature of 1.1 K. We develop a model based on spin-valley mixing and find that Johnson noise and two-phonon processes limit relaxation at low and high temperature, respectively. We also investigate the effect of temperature on charge noise and find a linear dependence up to 4 K. These results contribute to the understanding of relaxation in silicon quantum dots and are promising for qubit operation at elevated temperatures.QCD/Veldhorst LabQCD/Vandersypen LabGeneralQID/Dobrovitski GroupQN/Vandersypen La

Distributed entanglement and teleportation on a quantum network

We report on the realization of a multi-node quantum network. Using the network, we have demonstrated three protocols; generation of a entangled state shared by all nodes, entanglement swapping and quantum teleportation between non-neighboring nodes.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.QID/Hanson LabQCD/Vandersypen LabALG/GeneralBUS/Quantum DelftQID/Wehner GroupQN/Borregaard groepQuantum Computer ScienceQN/Hanson La