Inductively coupled plasma (ICP) etch rates for GaN are reported as a function of plasma pressure, plasma chemistry, rf power, and ICP power. Using a Cl2/H2/Ar plasma chemistry, GaN etch rates as high as 6875 Å/min are reported. The GaN surface morphology remains smooth over a wide range of plasma conditions as quantified using atomic force microscopy. Several etch conditions yield highly anisotropic profiles with smooth sidewalls. These results have direct application to the fabrication of group-III nitride etched laser facets.

We present cavity QED experiments with an Er 3+ :Y2SiO5 (Er:YSO) crystal magnetically coupled to a 3D cylindrical sapphire loaded copper resonator. Such waveguide cavities are promising for the realization of a superconducting quantum processor. Here, we demonstrate the coherent integration of a rare-earth spin ensemble with the 3D architecture. The collective coupling strength of the Er 3+ spins to the 3D cavity is 21 MHz. The cylindrical sapphire loaded resonator allowed us to explore the anisotropic collective coupling between the rare-earth doped crystal and the cavity. This work shows the potential of spin doped solids in 3D quantum circuits for application as microwave quantum memories as well as for prospective microwave to optical interfaces.Today, the field of quantum information science is looking for the possible physical and technological realization of future quantum processors. A considerable attention is focused on the study of isolated quantum systems such as trapped ions, electronic and nuclear spins, optical photons and superconducting (SC) quantum circuits. A promising route towards the realization of a feasible technology lies in the coherent integration of different systems resulting in hybrid quantum system [1]. Such a hybrid system will benefit from the best physical features of its isolated parts, as for instance, scalability and rapid manipulation of SC qubits, and long coherence time of atoms [2, 3].One way of implementing a hybrid quantum system, is to couple atomic ensembles magnetically to a planar superconducting quantum circuit [3]. Here, the strong confinement of a resonator mode along a coplanar microwave line mediates a strong collective coupling between the spins of the trapped atoms and the SC resonator. In spite of the persisting development of experiments on coupling trapped rubidium atoms to planar SC circuits, the SC hybrid circuits based on trapped atoms are still challenging to realize in practice [4,5]. In that respect, crystals doped with magnetic ions (nitrogen vacancy centers in diamond or rare-earth ion doped solids) are an appealing alternative atomic system [6][7][8][9][10][11][12]. Such solid states spin systems can easily be integrated with various planar SC quantum circuits.In contrast to the long coherence times of spin systems [13,14], the coherence of modern SC planar circuits is still limited by few microseconds, due to uncontrollable coupling to the environment [15]. The drastic improvement in coherence is possible by introducing a new architecture for SC quantum circuits based on threedimensional resonators, which has been recently proposed and successfully implemented [16,17]. Two-qubit gate operations have been demonstrated [18], and multiqubit entanglement schemes in 3D circuit QED have been proposed [19].From the perspective of electron spin resonance (ESR) spectroscopy, 3D cavities are used since the beginning of the field. It is also known, that a paramagnetic material with a very narrow inhomogeneous spin linewidth Γ 2 /2π (∼ 100 kHz at the microwav...

Reactively sputtered AlN is shown by electrical characterization of Pt/Au Schottky diodes to be an effect encapsulant for GaN annealed at 1100 °C. Schottky diodes formed on GaN encapsulated with AlN during the anneal had low reverse leakage currents with breakdown voltages in excess of 40 V. In contrast, samples annealed without the AlN layer had 3–4 orders-of-magnitude higher reverse leakage currents. Atomic force microscopy images of as-grown and annealed samples also demonstrate an increase in surface roughness and a change in morphology of the uncapped samples following annealing. Auger electron spectroscopy supports the hypothesis that the AlN encapsulant is reducing N loss from the GaN substrate. N loss in the uncapped samples is expected to create an n+-region at the surface that accounts for the high reverse leakage current and improved Ohmic behavior for the uncapped samples. The use of AlN encapsulation will enable the realization of all ion implanted GaN metal semiconductor field effect transistors.

Quantum memories are integral parts of both quantum computers and quantum communication networks. Naturally, such a memory is embedded into a hybrid quantum architecture, which has to meet the requirements of fast gates, long coherence times and long distance communication. Erbium doped crystals are well suited as a microwave quantum memory for superconducting circuits with additional access to the optical telecom C-band around 1.55 µm. Here, we report on circuit QED experiments with an Er 3+ :YAlO3 crystal and demonstrate strong coupling to a superconducting lumped element resonator. The low magnetic anisotropy of the host crystal allows for attaining the strong coupling regime at relatively low magnetic fields, which are compatible with superconducting circuits. In addition, Ce 3+ impurities were detected in the crystal, which showed strong coupling as well.PACS numbers: 42.50. Fx, 76.30.Kg, 03.67.Hk, 03.67.Lx, Reliable operation of quantum information and communication protocols requires a quantum memory (QM), i.e. a system, which allows for storage and on-demand retrieval of a quantum bit [1,2]. This can be realized by a great variety of physical systems such as single trapped ions [3], atoms [4], single spins [5], two-level defects [6] and spin-ensembles [7], which differ by their frequency band, coherence time and operating conditions. Rare-earth (RE) ions doped into a solid represent one of most promising systems suitable for quantum memories, because their inner shell 4f optical electronic transitions possess very long coherence times [8]. The excellent optical properties of RE doped crystals are confirmed and harvested by the world wide research in quantum optics. This includes a light-matter interface at the single photon level [9], an efficient and broadband quantum memory for light [10,11], a quantum memory at the telecom Cband [12], an atomic frequency comb memory [13], storage of entanglement in a RE doped crystal [14] and generation of entanglement between two crystals [15]. Yet, in contrast to the single atom approach, a quantum memory based on RE doped solids allows for the implementation of multimode storage protocols [16,17].There are seven RE's ions (Ce 3+ , Nd 3+ , Sm 3+ , Gd 3+ , Dy 3+ , Er 3+ , Yb 3+ ), which are suited for a microwave quantum memory due to the presence of a large electronic spin associated with an unquenched orbital moment [18]. Most of them have access to the nuclear spin degrees of freedom, which allow for long term storage [19]. These RE ions can be doped into a variety of host crystals, and therefore, can potentially be integrated with superconducting (SC) quantum circuits [20]. The resulting hybrid quantum system can consist of a SC qubit, a transmission line or a resonator magnetically coupled to the spin ensemble [21]. The exclusive feature of some RE ions (Nd 3+ , Er 3+ , Yb 3+ ) is the presence of optical transitions inside standard telecommunication bands. A quantum memory based on these RE elements can be very attractive for quantum communication between qubits...

Determining the state of a qubit on a timescale much shorter than its relaxation time is an essential requirement for quantum information processing. With the aid of a new type of nondegenerate parametric amplifier, we demonstrate the continuous detection of quantum jumps of a transmon qubit with 90 % fidelity in state discrimination. Entirely fabricated with standard two-step optical lithography techniques, this type of parametric amplifier consists of a dispersion engineered Josephson junction (JJ) array. By using long arrays, containing 10 3 JJs, we can obtain amplification at multiple eigenmodes with frequencies below 10 GHz, which is the typical range for qubit readout. Moreover, by introducing a moderate flux tunability of each mode, employing superconducting quantum interference device (SQUID) junctions, a single amplifier device could potentially cover the entire frequency band between 1 and 10 GHz.