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Register a new userStamping single wall nanotubes for circuit quantum electrodynamics
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We report on a dry transfer technique for single wall carbon nanotube devices which allows to embed them in high finesse microwave cavity. We demonstrate the ground state charge readout and a quality factor of about 3000 down to the single photon regime. This technique allows to make devices such as double quantum dots which could be instrumental for achieving the strong spin photon coupling. It can easily be extended to generic carbon nanotube based microwave devices.
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We present a simple technique which uses a self-aligned oxide etch to suspend individual single-wall carbon nanotubes between metallic electrodes. This enables one to compare the properties of a particular nanotube before and after suspension, as well as to study transport in suspended tubes. As an example of the utility of the technique, we study quantum dots in suspended tubes, finding that their capacitances are reduced owing to the removal of the dielectric substrate.
We theoretically study single and two-qubit dynamics in the circuit QED architecture. We focus on the current experimental design [Wallraff et al., Nature 431, 162 (2004); Schuster et al., Nature 445, 515 (2007)] in which superconducting charge qubits are capacitively coupled to a single high-Q superconducting coplanar resonator. In this system, logical gates are realized by driving the resonator with microwave fields. Advantages of this architecture are that it allows for multi-qubit gates between non-nearest qubits and for the realization of gates in parallel, opening the possibility of fault-tolerant quantum computation with superconduting circuits. In this paper, we focus on one and two-qubit gates that do not require moving away from the charge-degeneracy `sweet spot. This is advantageous as it helps to increase the qubit dephasing time and does not require modification of the original circuit QED. However these gates can, in some cases, be slower than those that do not use this constraint. Five types of two-qubit gates are discussed, these include gates based on virtual photons, real excitation of the resonator and a gate based on the geometric phase. We also point out the importance of selection rules when working at the charge degeneracy point.
Cavity quantum electrodynamics allows one to study the interaction between light and matter at the most elementary level. The methods developed in this field have taught us how to probe and manipulate individual quantum systems like atoms and superconducting quantum bits with an exquisite accuracy. There is now a strong effort to extend further these methods to other quantum systems, and in particular hybrid quantum dot circuits. This could turn out to be instrumental for a noninvasive study of quantum dot circuits and a realization of scalable spin quantum bit architectures. It could also provide an interesting platform for quantum simulation of simple fermion-boson condensed matter systems. In this short review, we discuss the experimental state of the art for hybrid circuit quantum electrodynamics with quantum dots, and we present a simple theoretical modeling of experiments.
Radiation sensors based on the heating effect of the absorbed radiation are typically relatively simple to operate and flexible in terms of the input frequency. Consequently, they are widely applied, for example, in gas detection, security, THz imaging, astrophysical observations, and medical applications. A new spectrum of important applications is currently emerging from quantum technology and especially from electrical circuits behaving quantum mechanically. This circuit quantum electrodynamics (cQED) has given rise to unprecedented single-photon detectors and a quantum computer supreme to the classical supercomputers in a certain task. Thermal sensors are appealing in enhancing these devices since they are not plagued by quantum noise and are smaller, simpler, and consume about six orders of magnitude less power than the commonly used traveling-wave parametric amplifiers. However, despite great progress in the speed and noise levels of thermal sensors, no bolometer to date has proven fast and sensitive enough to provide advantages in cQED. Here, we experimentally demonstrate a bolometer surpassing this threshold with a noise equivalent power of $30, rm{zW}/sqrt{rm{Hz}}$ on par with the current record while providing two-orders of magnitude shorter thermal time constant of 500 ns. Importantly, both of these characteristic numbers have been measured directly from the same device, which implies a faithful estimation of the calorimetric energy resolution of a single 30-GHz photon. These improvements stem from the utilization of a graphene monolayer as the active material with extremely low specific heat. The minimum demonstrated time constant of 200 ns falls greatly below the state-of-the-art dephasing times of roughly 100 {mu}s for superconducting qubits and meets the timescales of contemporary readout schemes thus enabling the utilization of thermal detectors in cQED.
Circuit quantum electrodynamics allows spatially separated superconducting qubits to interact via a quantum bus, enabling two-qubit entanglement and the implementation of simple quantum algorithms. We combine the circuit quantum electrodynamics architecture with spin qubits by coupling an InAs nanowire double quantum dot to a superconducting cavity. We drive single spin rotations using electric dipole spin resonance and demonstrate that photons trapped in the cavity are sensitive to single spin dynamics. The hybrid quantum system allows measurements of the spin lifetime and the observation of coherent spin rotations. Our results demonstrate that a spin-cavity coupling strength of 1 MHz is feasible.
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