Transferring the state of an information carrier from a sender to a receiver
is an essential primitive in both classical and quantum communication and
information processing. In a quantumprocess known as teleportation the unknown
state of a quantum bit can be relayed to a distant party using shared
entanglement and classical information. Here we present experiments in a
solid-state system based on superconducting quantum circuits demonstrating the
teleportation of the state of a qubit at the macroscopic scale. In our
experiments teleportation is realized deterministically with high efficiency
and achieves a high rate of transferred qubit states. This constitutes a
significant step towards the realization of repeaters for quantum communication
at microwave frequencies and broadens the tool set for quantum information
processing with superconducting circuits.
We make use of a superconducting qubit to study the effects of noise on
adiabatic geometric phases. The state of the system, an effective spin one-half
particle, is adiabatically guidedalong a closed path in parameter space and
thereby acquires a geometric phase. By introducing artificial fluctuations in
the control parameters, we measure the geometric contribution to dephasing for
a variety of noise powers and evolution times. Our results clearly show that
only fluctuations which distort the path lead to geometric dephasing. In a
direct comparison with the dynamic phase, which is path-independent, we observe
that the adiabatic geometric phase is less affected by noise-induced dephasing.
This observation directly points towards the potential of geometric phases for
quantum gates or metrological applications.
Interference at a beam splitter reveals both classical and quantum properties
of electromagnetic radiation. When two indistinguishable single photons impinge
at the two inputs of abeam splitter they coalesce into a pair of photons
appearing in either one of its two outputs. This effect is due to the bosonic
nature of photons and was first experimentally observed by Hong, Ou, and Mandel
(HOM) [1]. Here, we present the observation of the HOM effect with two
independent single-photon sources in the microwave frequency domain. We probe
the indistinguishability of single photons, created with a controllable delay,
in time-resolved second-order cross- and auto-correlation function
measurements. Using quadrature amplitude detection we are able to resolve
different photon numbers and detect coherence in and between the output arms.
This measurement scheme allows us to observe the HOM effect and, in addition,
to fully characterize the two-mode entanglement of the spatially separated beam
splitter output modes. Our experiments constitute a first step towards using
two-photon interference at microwave frequencies for quantum communication and
information processing, e.g. for distributing entanglement between nodes of a
quantum network [2, 3] and for linear optics quantum computation [4, 5].
Interference at a beam splitter reveals both classical and quantum properties of electromagnetic radiation. When two indistinguishable single photons impinge at the two inputs of abeam splitter they coalesce into a pair of photons appearing in either one of its two outputs. This effect is due to the bosonic nature of photons and was first experimentally observed by Hong, Ou, and Mandel (HOM) [1]. Here, we present the observation of the HOM effect with two independent single-photon sources in the microwave frequency domain. We probe the indistinguishability of single photons, created with a controllable delay, in time-resolved second-order cross- and auto-correlation function measurements. Using quadrature amplitude detection we are able to resolve different photon numbers and detect coherence in and between the output arms. This measurement scheme allows us to observe the HOM effect and, in addition, to fully characterize the two-mode entanglement of the spatially separated beam splitter output modes. Our experiments constitute a first step towards using two-photon interference at microwave frequencies for quantum communication and information processing, e.g. for distributing entanglement between nodes of a quantum network [2, 3] and for linear optics quantum computation [4, 5].
Geometric phases, which accompany the evolution of a quantum system and
depend only on its trajectory in state space, are commonly studied in two-level
systems. Here, however, we studythe adiabatic geometric phase in a weakly
anharmonic and strongly driven multi-level system, realised as a
superconducting transmon-type circuit. We measure the contribution of the
second excited state to the two-level geometric phase and find good agreement
with theory treating higher energy levels perturbatively. By changing the
evolution time, we confirm the independence of the geometric phase of time and
explore the validity of the adiabatic approximation at the transition to the
non-adiabatic regime.