On-demand single-electron transfer between distant quantum dots R. P. G. McNeil, M. Kataoka, C. J. B. Ford, C. H. W. Barnes, D. Anderson, G. A. C. Jones, I. Farrer, and D. A. Ritchie

Single-electron circuits of the future, consisting of a network of quantum
dots, will require a mechanism to transport electrons from one functional part
to another. For example, in a quantum computer[1] decoherence and circuit
complexity can be reduced by separating qubit manipulation from measurement and
by providing some means to transport electrons from one to the other.[2]
Tunnelling between neighbouring dots has been demonstrated[3, 4] with great
control, and the manipulation of electrons in single and double-dot systems is
advancing rapidly.[5-8] For distances greater than a few hundred nanometres
neither free propagation nor tunnelling are viable whilst maintaining
confinement of single electrons. Here we show how a single electron may be
captured in a surface acoustic wave minimum and transferred from one quantum
dot to a second unoccupied dot along a long empty channel. The transfer
direction may be reversed and the same electron moved back and forth over sixty
times without error, a cumulative distance of 0.25 mm. Such on-chip transfer
extends communication between quantum dots to a range that may allow the
integration of discrete quantum information-processing components and devices.

Macroscopic Supercurrents through a Silicon Surface Reconstruction with Atomic Steps Takashi Uchihashi, Puneet Mishra, Masakazu Aono, and Tomonobu Nakayama

Macroscopic and robust supercurrents are observed by direct electron
transport measurements on a silicon surface reconstruction with In adatoms
(Si(111)-(R7xR3)-In). The superconducting transition manifests itself as an
emergence of the zero resistance state below 2.8 K. $I-V$ characteristics
exhibit sharp and hysteretic switching between superconducting and normal
states with well-defined critical and retrapping currents. The two-dimensional
(2D) critical current density $J_\mathrm{2D,c}$ is estimated to be as high as
$1.8 \times 10^{-2} \ \mathrm{A/m}$ at 1.8 K. The temperature dependence of
$J_\mathrm{2D,c}$ indicates that the surface atomic steps play the role of
strongly coupled Josephson junctions.

Observation of spin-selective tunneling in SiGe nanocrystals G. Katsaros, V. N. Golovach, P. Spathis, N. Ares, M. Stoffel, F. Fournel, O. G. Schmidt, L. I. Glazman, and S. De Franceschi

Spin-selective tunneling of holes in SiGe nanocrystals contacted by
normal-metal leads is reported. The spin selectivity arises from an interplay
of the orbital effect of the magnetic field with the strong spin-orbit
interaction present in the valence band of the semiconductor. We demonstrate
both experimentally and theoretically that spin-selective tunneling in
semiconductor nanostructures can be achieved without the use of ferromagnetic
contacts. The reported effect, which relies on mixing the light and heavy
holes, should be observable in a broad class of quantum-dot systems formed in
semiconductors with a degenerate valence band.

Theory of the ground state spin of the NV- center in diamond: I. Fine structure, hyperfine structure, and interactions with electric, magnetic and strain fields M.W. Doherty, F. Dolde, H. Fedder, F. Jelezko, J. Wrachtrup, N.B. Manson and L.C.L. Hollenberg

The ground state spin of the negatively charged nitrogen-vacancy center in
diamond has been the platform for the recent rapid expansion of new frontiers
in quantum metrology and solid state quantum information processing. In ambient
conditions, the spin has been demonstrated to be a high precision magnetic and
electric field sensor as well as a solid state qubit capable of coupling with
nearby nuclear and electronic spins. However, in spite of its many outstanding
demonstrations, the theory of the spin has not yet been fully developed and
there does not currently exist thorough explanations for many of its
properties, such as the anisotropy of the electron g-factor and the existence
of Stark effects and strain splittings. In this work, the theory of the ground
state spin is fully developed for the first time using the molecular orbital
theory of the center in order to provide detailed explanations for the spin’s
fine and hyperfine structures and its interactions with electric, magnetic and
strain fields.

Dissipation and Ultrastrong Coupling in Circuit QED F\’elix Beaudoin, J. M. Gambetta and A. Blais

Cavity and circuit QED study light-matter interaction at its most fundamental
level. Yet, this interaction is most often neglected when considering the
coupling of this system with an environment. In this paper, we show how this
simplification, which leads to the standard quantum optics master equation, is
at the root of unphysical effects. Including qubit relaxation and dephasing,
and cavity relaxation, we derive a master equation that takes into account the
qubit-resonator coupling. Special attention is given to the ultrastrong
coupling regime, where the failure of the quantum optical master equation is
manifest. In this situation, our model predicts an asymmetry in the vacuum Rabi
splitting that could be used to probe dephasing noise at unexplored
frequencies. We also show how fluctuations in the qubit frequency can cause
sideband transitions, squeezing, and Casimir-like photon generation.

Vertical Field-Effect Transistor Based on Wavefunction Extension Adam Sciambi, Matthew Pelliccione, Michael P. Lilly, Seth R. Bank, Arthur C. Gossard, Loren N. Pfeiffer, Ken W. West, David Goldhaber-Gordon

Quantum-coherent coupling of a mechanical oscillator to an optical cavity mode E. Verhagen, S. Del\’eglise, S. Weis, A. Schliesser, and T. J. Kippenberg

Quantum control of engineered mechanical oscillators can be achieved by
coupling the oscillator to an auxiliary degree of freedom, provided that the
coherent rate of energy exchange exceeds the decoherence rate of each of the
two sub-systems. We achieve such quantum-coherent coupling between the
mechanical and optical modes of a micro-optomechanical system. Simultaneously,
the mechanical oscillator is cooled to an average occupancy of n = 1.7 \pm 0.1
motional quanta. Pulsed optical excitation reveals the exchange of energy
between the optical light field and the micromechanical oscillator in the time
domain at the level of less than one quantum on average. These results provide
a route towards the realization of efficient quantum interfaces between
mechanical oscillators and optical fields.

Attojoule all-optical switching with a single quantum dot Deepak Sridharan, Ranojoy Bose, Hyochul Kim Glenn S. Solomon, and Edo Waks

We experimentally investigate the dynamic nonlinear response of a single
quantum dot (QD) strongly coupled to a photonic crystal cavity-waveguide
structure. The temporal response is measured by pump-probe excitation where a
control pulse propagating through the waveguide is used to create an optical
Stark shift on the QD, resulting in a large modification of the cavity
reflectivity. This optically induced cavity reflectivity modification switches
the propagation direction of a detuned signal pulse. Using this device we
demonstrate all-optical switching with only 14 attojoules of control pulse
energy. The response time of the switch is measured to be up to 8.4 GHz, which
is primarily limited by the cavity-QD interaction strength.

Immunity of information encoded in decoherence-free subspaces to particle loss Piotr Migda{\l}, Konrad Banaszek

We demonstrate that for an ensemble of qudits, subjected to collective
decoherence in the form of perfectly correlated random SU(d) unitaries, quantum
superpositions stored in the decoherence free subspace are fully immune against
the removal of one particle. This provides a feasible scheme to protect quantum
information encoded in the polarization state of a sequence of photons against
both collective depolarization and one photon loss, and can be demonstrated
with photon quadruplets using currently available technology.

A micropillar for cavity optomechanics A. G. Kuhn (LKB – Jussieu), M. Bahriz (DMPH), O. Ducloux (DMPH), C. Chartier (DMPH), O. Le Traon (DMPH), T. Briant (LKB – Jussieu), P. -F. Cohadon (LKB – Jussieu), A. Heidmann (LKB – Jussieu), C. Michel (LMA), L. Pinard (LMA), R. Flaminio (LMA)

We present a new micromechanical resonator designed for cavity optomechanics.
We have used a micropillar geometry to obtain a high-frequency mechanical
resonance with a low effective mass and a very high quality factor. We have
coated a 60-$\mu$m diameter low-loss dielectric mirror on top of the pillar and
are planning to use this micromirror as part of a high-finesse Fabry-Perot
cavity, to laser cool the resonator down to its quantum ground state and to
monitor its quantum position fluctuations by quantum-limited optical
interferometry.

Mechanically Compliant Grating Reflectors for Optomechanics Utku Kemiktarak, Michael Metcalfe, Mathieu Durand and John Lawall

We demonstrate micromechanical reflectors with a reflectivity as large as
99.4% and a mechanical quality factor Q as large as 7.8*10^5 for optomechanical
applications. The reflectors are silicon nitride membranes patterned with
sub-wavelength grating structures, obviating the need for the many dielectric
layers used in conventional mirrors. We have employed the reflectors in the
construction of a Fabry-Perot cavity with a finesse as high as F=1200, and used
the optical response to probe the mechanical properties of the membrane. By
driving the cavity with light detuned to the high-frequency side of a cavity
resonance, we create an optical antidamping force that causes the reflector to
self-oscillate at 211 kHz.

An introduction to reliable quantum computation Panos Aliferis

Structure of 2D Topological Stabilizer Codes H. Bombin

We provide a detailed study of the general structure of two-dimensional
topological stabilizer quantum error correcting codes, including subsystem
codes. Under the sole assumption of translational invariance, we show that all
such codes can be understood in terms of the homology of string operators that
carry a certain topological charge. In the case of subspace codes, we prove
that two codes are equivalent under a suitable set of local transformations if
and only they have equivalent topological charges. Our approach emphasizes
local properties of the codes over global ones.

Decoherence Suppression by Cavity Optomechanical Cooling Eyal Buks

We consider a cavity optomechanical cooling configuration consisting of a
mechanical resonator (denoted as resonator b) and an electromagnetic resonator
(denoted as resonator a), which are coupled in such a way that the effective
resonance frequency of resonator a depends linearly on the displacement of
resonator b. We study whether back-reaction effects in such a configuration can
be efficiently employed for suppression of decoherence. To that end, we
consider the case where the mechanical resonator is prepared in a superposition
of two coherent states and evaluate the rate of decoherence. We find that no
significant suppression of decoherence is achievable when resonator a is
assumed to have a linear response. On the other hand, when resonator a exhibits
Kerr nonlinearity and/or nonlinear damping the decoherence rate can be made
much smaller than the equilibrium value provided that the parameters that
characterize these nonlinearities can be tuned close to some specified optimum
values.