8 research outputs found
Demonstration of conditional gate operation using superconducting charge qubits
Since the first demonstration of coherent control of a quantum state of a
superconducting charge qubit a variety of Josephson-junction-based qubits have
been implemented with remarkable progress in coherence time and read-out
schemes. Although the current level of this solid-state device is still not as
advanced as that of the most advanced microscopic-system-based qubits, these
developments, together with the potential scalability, have renewed its
position as a strong candidate as a building block for the quantum computer.
Recently, coherent oscillation and microwave spectroscopy in
capacitively-coupled superconducting qubits have been reported. The next
challenging step toward quantum computation is a realization of logic gates.
Here we demonstrate a conditional gate operation using a pair of coupled
superconducting charge qubits. Using a pulse technique, we prepare different
input states and show that they can be transformed by controlled-NOT (C-NOT)
gate operation in the amplitude of the states. Although the phase evolution
during the gate operation is still to be clarified, the present results are a
major step toward the realization of a universal solid-state quantum gate
Superconducting Nanocircuits for Topologically Protected Qubits
For successful realization of a quantum computer, its building blocks
(qubits) should be simultaneously scalable and sufficiently protected from
environmental noise. Recently, a novel approach to the protection of
superconducting qubits has been proposed. The idea is to prevent errors at the
"hardware" level, by building a fault-free (topologically protected) logical
qubit from "faulty" physical qubits with properly engineered interactions
between them. It has been predicted that the decoupling of a protected logical
qubit from local noises would grow exponentially with the number of physical
qubits. Here we report on the proof-of-concept experiments with a prototype
device which consists of twelve physical qubits made of nanoscale Josephson
junctions. We observed that due to properly tuned quantum fluctuations, this
qubit is protected against magnetic flux variations well beyond linear order,
in agreement with theoretical predictions. These results demonstrate the
feasibility of topologically protected superconducting qubits.Comment: 25 pages, 5 figure
Local probing of propagating acoustic waves in a gigahertz echo chamber
In the same way that micro-mechanical resonators resemble guitar strings and drums, surface acoustic waves resemble the sound these instruments produce, but moving over a solid surface rather than through air. In contrast with oscillations in suspended resonators, such propagating mechanical waves have not before been studied near the quantum mechanical limits. Here, we demonstrate local probing of surface acoustic waves with a displacement sensitivity of 30 amRMS Hz^(−1/2) and detection sensitivity on the single-phonon level after averaging, at a frequency of 932 MHz. Our probe is a piezoelectrically coupled single-electron transistor, which is sufficiently fast, non-destructive and localized to enable us to track pulses echoing back and forth in a long acoustic cavity, self-interfering and ringing the cavity up and down. We project that strong coupling to quantum circuits will enable new experiments, and hybrids using the unique features of surface acoustic waves. Prospects include quantum investigations of phonon–phonon interactions, and acoustic coupling to superconducting qubits for which we present favourable estimates