Double quantum dots as a high sensitive submillimeter-wave detector

A single electron transistor (SET) consisting of parallel double quantum dots fabricated in a GaAs/Al$_{x}$Ga$_{1-x}$As heterostructure crystal is demonstrated to serve as an extremely high sensitive detector of submillimeter waves (SMMW). One of the double dots is ionized by SMMW via Kohn-mode plasma excitation, which affects the SET conductance through the other quantum dot yielding the photoresponse. Noise equivalent power of the detector for wavelengths about 0.6 mm is estimated to reach the order of $10^{-17}$ W/$\sqrt{Hz}$ at 70 mK.Comment: 3 pages, 4 figures, REVTeX, submitted to Appl.Phys.Let

Quantum noise in the Josephson charge qubit

We study decoherence of the Josephson charge qubit by measuring energy relaxation and dephasing with help of the single-shot readout. We found that the dominant energy relaxation process is a spontaneous emission induced by quantum noise coupled to the charge degree of freedom. Spectral density of the noise at high frequencies is roughly proportional to the qubit excitation energy.Comment: Submitted to Phys. Rev. Letter

Parity effect in superconducting aluminum single electron transistors with spatial gap profile controlled by film thickness

We propose a novel method for suppression of quasiparticle poisoning in Al Coulomb blockade devices. The method is based on creation of a proper energy gap profile along the device. In contrast to the previously used techniques, the energy gap is controlled by the film thickness. Our transport measurements confirm that the quasiparticle poisoning is suppressed and clear 2$e$ periodicity is observed only when the island is made much thinner than the leads. This result is consistent with the existing model and provides a simple method to suppress quasiparticle poisoning

Signal amplification in a qubit-resonator system

We study the dynamics of a qubit-resonator system, when the resonator is driven by two signals. The interaction of the qubit with the high-amplitude driving we consider in terms of the qubit dressed states. Interaction of the dressed qubit with the second probing signal can essentially change the amplitude of this signal. We calculate the transmission amplitude of the probe signal through the resonator as a function of the qubit's energy and the driving frequency detuning. The regions of increase and attenuation of the transmitted signal are calculated and demonstrated graphically. We present the influence of the signal parameters on the value of the amplification, and discuss the values of the qubit-resonator system parameters for an optimal amplification and attenuation of the weak probe signal.Comment: 7 pages, 8 figure

Temperature square dependence of the low frequency 1/f charge noise in the Josephson junction qubits

To verify the hypothesis about the common origin of the low frequency 1/f noise and the quantum f noise recently measured in the Josephson charge qubits, we study temperature dependence of the 1/f noise and decay of coherent oscillations. T^2 dependence of the 1/f noise is experimentally demonstrated, which supports the hypothesis. We also show that dephasing in the Josephson charge qubits off the electrostatic energy degeneracy point is consistently explained by the same low frequency 1/f noise that is observed in the transport measurements.Comment: 4 pages, 2 figure

Resonance Fluorescence of a Single Artificial Atom

An atom in open space can be detected by means of resonant absorption and reemission of electromagnetic waves, known as resonance fluorescence, which is a fundamental phenomenon of quantum optics. We report on the observation of scattering of propagating waves by a single artificial atom. The behavior of the artificial atom, a superconducting macroscopic two-level system, is in a quantitative agreement with the predictions of quantum optics for a pointlike scatterer interacting with the electromagnetic field in one-dimensional open space. The strong atom-field interaction as revealed in a high degree of extinction of propagating waves will allow applications of controllable artificial atoms in quantum optics and photonics.Comment: 5 pages, 4 figure

Quantum behaviour of a flux qubit coupled to a resonator

We present a detailed theoretical analysis for a system of a superconducting flux qubit coupled to a transmission line resonator. The master equation, accounting incoherent processes for a weakly populated resonator, is analytically solved. An electromagnetic wave transmission coefficient through the system, which provides a tool for probing dressed states of the qubit, is derived. We also consider a general case for the resonator with more than one photon population and compare the results with an experiment on the qubit-resonator system in the intermediate coupling regime, when the coupling energy is comparable with the qubit relaxation rate.Comment: 16 pages, 6 figure

Electromagnetically induced transparency on a single artificial atom

We present experimental observation of electromagnetically induced transparency (EIT) on a single macroscopic artificial "atom" (superconducting quantum system) coupled to open 1D space of a transmission line. Unlike in a optical media with many atoms, the single atom EIT in 1D space is revealed in suppression of reflection of electromagnetic waves, rather than absorption. The observed almost 100 % modulation of the reflection and transmission of propagating microwaves demonstrates full controllability of individual artificial atoms and a possibility to manipulate the atomic states. The system can be used as a switchable mirror of microwaves and opens a good perspective for its applications in photonic quantum information processing and other fields