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A broad range of scientific and industrial disciplines require precise optical measurements at very low light levels. Single-photon detectors combining high efficiency and high time resolution are pivotal in such experiments. By using relatively thick films of NbTiN (8-11 nm) and improving the pattern fidelity of the nanostructure of the superconducting nanowire single-photon detectors (SNSPD), we fabricated devices demonstrating superior performance over all previously reported detectors in the combination of efficiency and time resolution. Our findings prove that small variations in the nanowire width, in the order of a few nanometers, can lead to a significant penalty on their temporal response. Addressing these issues, we consistently achieved high time resolution (best device 7.7 ps, other devices a10-16 ps) simultaneously with high system detection efficiencies (80-90%) in the wavelength range of 780-1000 nm, as well as in the telecom bands (1310-1550 nm). The use of thicker films allowed us to fabricate large-area multipixel devices with homogeneous pixel performance. We first fabricated and characterized a 100 × 100 μm2 16-pixel detector and showed there was little variation among individual pixels. Additionally, to showcase the power of our platform, we fabricated and characterized 4-pixel multimode fiber-coupled detectors and carried out photon-correlation experiments on a nanowire quantum dot resulting in g2(0) values lower than 0.04. The multipixel detectors alleviate the need for beamsplitters and can be used for higher order correlations with promising prospects not only in the field of quantum optics, but also in bioimaging applications, such as fluorescence microscopy and positron emission tomography.

Future quantum computers capable of solving relevant problems will require a large number of qubits that can be operated reliably. However, the requirements of having a large qubit count and operating with high-fidelity are typically conflicting. Spins in semiconductor quantum dots show long-term promise but demonstrations so far use between one and four qubits and typically optimize the fidelity of either single- or two-qubit operations, or initialization and readout. Here we increase the number of qubits and simultaneously achieve respectable fidelities for universal operation, state preparation and measurement. We design, fabricate and operate a six-qubit processor with a focus on careful Hamiltonian engineering, on a high level of abstraction to program the quantum circuits and on efficient background calibration, all of which are essential to achieve high fidelities on this extended system. State preparation combines initialization by measurement and real-time feedback with quantum-non-demolition measurements. These advances will allow for testing of increasingly meaningful quantum protocols and constitute a major stepping stone towards large-scale quantum computers., 38 pages (including supplementary material)

Superconducting nanowire single photon detectors (SNSPDs) have become a mature technology for single-photon detection with excellent performance [...]

The requirements in quantum optics experiments for high single-photon detection efficiency. low timing jitter, low dark count rate and short dead time have been fulfilled with the development of superconducting nanowire single-photon detectors. Although they offer a detection efficiency above 90%, achieving a high time resolution in devices made of amorphous materials is a challenge, particularly at temperatures above 0.8 K. Devices made from niobium nitride and niobium titanium nitride allow us to reach the best timing jitter but. in turn, have stronger requirements in terms of film quality to achieve a high efficiency. Here we take advantage of the flexibility of reactive co-sputter deposition to tailor the composition of NbxTi1-xN superconducting films and show that a Nb fraction of x = 0.62 allows for the fabrication of detectors from films as thick as 9 nm and covering an active area of 20 mu m. with a wide detection saturation plateau at telecom wavelengths and in particular at 1550 nm. This is a signature of an internal detection efficiency saturation, achieved while maintaining the high time resolution associated with NbTiN and operation at 2.5K. With our optimized recipe, we reliably fabricated detectors with high critical current densities reaching a saturation plateau at 1550 nm with 80% system detection efficiency and with a FWHM timing jitter as low as 19.5 ps. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

We demonstrate the strong coupling between a single electron spin in silicon and a single photon in a superconducting microwave cavity. Using the same cavity we perform rapid high-fidelity single-shot readout of two-electron spin states.

We experimentally investigate the performance of NbTiN superconducting nanowire single photon detectors above the base temperature of a conventional Gifford-McMahon cryocooler (2.5 K). By tailoring design and thickness (8 - 13 nm) of the detectors, high performance, high operating temperature, single-photon detection from the visible to telecom wavelengths are demonstrated. At 4.3 K, a detection efficiency of 82 % at 785 nm wavelength and a timing jitter of 30 ± 0.3 ps are achieved. In addition, for 1550 nm and similar operating temperature we measured a detection efficiency as high as 64 %. Finally, we show that at temperatures up to 7 K, unity internal efficiency is maintained for the visible spectrum. Our work is particularly important to allow for the large scale implementation of superconducting single photon detectors in combination with heat sources such as free-space optical windows, cryogenic electronics, microwave sources and active optical components for complex quantum optical experiments and bio-imaging.

Silicon spin qubits are one of the leading platforms for quantum computation1,2. As with any qubit implementation, a crucial requirement is the ability to measure individual quantum states rapidly and with high fidelity. Since the signal from a single electron spin is minute, the different spin states are converted to different charge states3,4. Charge detection, so far, has mostly relied on external electrometers5?7, which hinders scaling to two-dimensional spin qubit arrays2,8,9. Alternatively, gate-based dispersive read-out based on off-chip lumped element resonators has been demonstrated10?13, but integration times of 0.2?2 ms were required to achieve single-shot read-out14?16. Here, we connect an on-chip superconducting resonant circuit to two of the gates that confine electrons in a double quantum dot. Measurement of the power transmitted through a feedline coupled to the resonator probes the charge susceptibility, distinguishing whether or not an electron can oscillate between the dots in response to the probe power. With this approach, we achieve a signal-to-noise ratio of about six within an integration time of only 1 ?s. Using Pauli?s exclusion principle for spin-to-charge conversion, we demonstrate single-shot read-out of a two-electron spin state with an average fidelity of >98% in 6 ?s. This result may form the basis of frequency-multiplexed read-out in dense spin qubit systems without external electrometers, therefore simplifying the system architecture. ? 2019, The Author(s), under exclusive licence to Springer Nature Limited.The spin state of electrons in a double quantum dot in silicon is read in a single shot with 98% average fidelity within 6 ?s by means of an on-chip superconducting resonator connected to two of the gates defining the double dot structure.

In this work, a novel hybrid fabrication method for graphene quantum dot devices with minimum feature sizes of ~3nm and high yield is described. It is a combination of e-beam lithography and direct milling with the sub-nm focused helium ion beam generated by a helium ion microscope. The method is used to fabricate graphene quantum dot devices contacted with metal to allow electrical characterization. An annealing step is described that reduces hydrocarbon contamination on the sample surface and allows complete removal of graphene by the helium ion beam and therefore successful isolation of side gates. The electrical characterization of the final device demonstrates the successful fabrication of the first electrically characterized He-ion beam patterned graphene device. The highly controllable, fine scale fabrication capabilities offered by this approach could lead to a more detailed understanding of the electrical characteristics of graphene quantum devices and pave the way towards room-temperature operable graphene quantum dot devices.

Helium ion beam lithography (HIL) has been demonstrated as a promising alternative to electron beam lithography (EBL) for R&D purposes, offering high-resolution lithography at high pattern densities. This chapter reviews focused He ion beam lithography, providing a detailed discussion on the ion beam-resist interaction mechanisms and latest experimental results in this field. In addition, impact of ion shot noise is examined, a comparison to He-ion beam milling is made, and future directions are mentioned.

In this paper we first present a new hybrid fabrication process of downscaled graphene nanodevices based on direct ultrafine milling process by using atomic-size helium ion beam and the electron beam lithography process. We then describe the bilayer graphene single carrier transistors (GSCTs) and their Coulomb oscillation characteristics at 1.7 K. Unique double current peak structures were observed in the Coulomb oscillation which are attributable to single carrier tunneling via vertically stacked double charging islands. Finally we demonstrate a mechanically stable graphene nano-electro-mechanical (GNEM) switch fabricated using a simple etching-free method with polymer sacrificial spacer. Switch-ON and OFF operations are achieved in a reversible manner.

In this paper we first present a new fabrication process of downscaled graphene nanodevices based on direct milling of graphene using an atomic-size helium ion beam. We address the issue of contamination caused by the electron-beam lithography process to pattern the contact metals prior to the ultrafine milling process in the helium ion microscope (HIM). We then present our recent experimental study of the effects of the helium ion exposure on the carrier transport properties. By varying the time of helium ion bombardment onto a bilayer graphene nanoribbon transistor, the change in the transfer characteristics is investigated along with underlying carrier scattering mechanisms. Finally we study the effects of various single defects introduced into extremely-scaled armchair graphene nanoribbons on the carrier transport properties using ab initio simulation.

In this paper we overview recent attempts at co-integrating silicon nano-electro-mechanical systems (NEMS) with nanoelectronic devices aiming to add more functionalities to conventional electronic devices in ‘More-than-Moore’ domain and also explore novel operating principles in ‘Beyond CMOS’ domain.