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In quantum optics, light–matter interaction has conventionally been studied using small atoms interacting with electromagnetic fields with wavelength several orders of magnitude larger than the atomic dimensions1,2. In contrast, here we experimentally demonstrate the vastly different ‘giant atom’ regime, where an artificial atom interacts with acoustic fields with wavelength several orders of magnitude smaller than the atomic dimensions. This is achieved by coupling a superconducting qubit3 to surface acoustic waves at two points with separation on the order of 100 wavelengths. This approach is comparable to controlling the radiation of an atom by attaching it to an antenna. The slow velocity of sound leads to a significant internal time-delay for the field to propagate across the giant atom, giving rise to non-Markovian dynamics4. We demonstrate the non-Markovian character of the giant atom in the frequency spectrum as well as non-exponential relaxation in the time domain. By coupling a superconducting qubit to surface acoustic waves the ‘giant atom’ regime is realized, where an atom is coupled to a field with wavelength orders of magnitude smaller than the atomic size. This leads to non-Markovian qubit dynamics.

One of the most surprising predictions of modern quantum theory is that the vacuum of space is not empty. In fact, quantum theory predicts that it teems with virtual particles flitting in and out of existence. While initially a curiosity, it was quickly realized that these vacuum fluctuations had measurable consequences, for instance producing the Lamb shift of atomic spectra and modifying the magnetic moment for the electron. This type of renormalization due to vacuum fluctuations is now central to our understanding of nature. However, these effects provide indirect evidence for the existence of vacuum fluctuations. From early on, it was discussed if it might instead be possible to more directly observe the virtual particles that compose the quantum vacuum. 40 years ago, Moore suggested that a mirror undergoing relativistic motion could convert virtual photons into directly observable real photons. This effect was later named the dynamical Casimir effect (DCE). Using a superconducting circuit, we have observed the DCE for the first time. The circuit consists of a coplanar transmission line with an electrical length that can be changed at a few percent of the speed of light. The length is changed by modulating the inductance of a superconducting quantum interference device (SQUID) at high frequencies (~11 GHz). In addition to observing the creation of real photons, we observe two-mode squeezing of the emitted radiation, which is a signature of the quantum character of the generation process., Comment: 12 pages, 3 figures

We describe in this review progress in techniques for measuring the quantum states of the single Cooper-pair box (SCB) at the Jet Propulsion Laboratory, and the use of these techniques to characterize their performance as quantum bits. Initially, the Radio-Frequency-Single-Electron Transistor was used to measure conventional and differential versions of the SCB. To overcome some of the difficulties associated with the radio-frequency single-electron transistor, a transition was made to readout based on the quantum capacitance technique. Using this method, entanglement between two SCBs was demonstrated spectroscopically and with ground state characterization.

We study decoherence of a Josephson charge qubit using fast pulses to perform qubit rotations. The gate charge dependence of the decoherence rate indicates that the low frequency fluctuations affecting the qubit are from charges distributed with a 1/f-type spectrum. Assuming the form Sq(ω) = α/|ω|, we find $$\sqrt \alpha$$ = 4 × 10−3e, which is slightly higher than the value found from very low frequency noise measurements. PACS numbers: 03.67.-a, 75.40.+r, 85.25.Cp.

An experimental configuration is analyzed in order to studyplasma modes in a superconducting wire deposited ontoSrTiO3. A dispersion relation has been derived byevaluating the effect of the environment surrounding the wire.It corresponds to the one-dimensional dispersion law predictedfor an isolated superconducting wire. Preliminary measurementsare presented. They show 1D plasma modes in theoptimized experimental configuration here studied.

We describe a new mode of operation of the single electron transistor (SET). The so-called RF-SET (radio frequency-SET) is a dual of the RF-SQUID (radio frequency-superconducting quantum interference device). It has been operated at frequencies above 100 MHz with a very high charge sensitivity (1.2 × 10−5 e/√Hz. The large bandwidth, combined with a high sensitivity, will enable studies of the dynamics of mesoscopic systems on very short time scales.

We report on measurements of the current-voltage characteristics of ultrasmall Josephson junctions. The junctions were made of either Al or Pb alloy, and the leads connecting the junctions to the outside world were high resistance thin film microstrips fabricated on the chip very close to the junction. The high frequency impedance of these leads was sufficiently large to enable the observation in a single Josephson junction of the Coulomb blockade of Cooper pair tunneling, as well as evidence for the time correlation of Cooper pair tunneling (Bloch Oscillations).

Although it is over 100 years since Millikan showed that electric charge is quantized, it is only with the development of a new generation of charge pumps that this fact can be used to define the fundamental unit of electrical current, the ampere.

We have fabricated two nominally identical one-dimensional arrays of small tunnel junctions, each with 10 junctions in series. Each electrode of one array is capacitively coupled to two electrodes in the other array. By measuring the current voltage characteristics of the two arrays simultaneously, we observe a coupling between the currents in the two arrays. In a narrow region of biasing conditions, we find that the currents are equally large but with opposite signs. We interprete this as correlated transport of electrons in one array, and holes in the other array. The experimental results show qualitative agreement with numerical simulations.

We have fabricated small high-ohmic resistors by anodic oxidation of Nb wires, monitoring and trimming the resistancein situ during the anodization. At millikelvin temperatures, the current-voltage characteristics of these resistors are nonlinear around zero bias. Wires with a low sheet resistance show a supercurrent feature, while higher resistive ones exhibit a sharp blockade that can be partially suppressed by external magnetic fields. The onset of a strong blockade occurs when the sheet resistance exceeds a value of the order of the resistance quantumh/(4e2).

We report on fabrication of a Coulomb blockade electrometer based on an ultrasmall YBa2Cu3O7-δ (YBCO) island coupled by tunnel junctions to two gold electrodes. At temperatures below 0.5 K the low bias conductance was suppressed by the Coulomb blockade. The blockade could periodically, be varied by the gate potential. An external magnetic field of up to 5 T strongly influenced the transport via the island but did not change the period of the gate voltage dependence.

New metallic glass alloys have been prepared by melt spinning of La−Si samples in a pumped system. The superconducting transition temperature,Tc, increases linearly with the La concentration, from 3.00 K at 73 at. % La to 3.80 K at 85 at. %. Three new metastable phases: α-, β-, and γ-La3Si, were formed by annealing and crystallizing amorphous La3Si. Their crystal structures are orthorhombic (a=6.32 A,b=8.06 A,c=9.96 A), hcp (a=10.55 A,c=5.05 A), and tetragonal (a=6.92 A,c=5.05 A) resp.Tc increased to 3.75 K, 6.00 K and 6.80 K, resp. During low temperature anneals of an amorphous La3Si alloy,Tc changed logarithmically with time.