4,997 research outputs found
Towards Quantum Repeaters with Solid-State Qubits: Spin-Photon Entanglement Generation using Self-Assembled Quantum Dots
In this chapter we review the use of spins in optically-active InAs quantum
dots as the key physical building block for constructing a quantum repeater,
with a particular focus on recent results demonstrating entanglement between a
quantum memory (electron spin qubit) and a flying qubit (polarization- or
frequency-encoded photonic qubit). This is a first step towards demonstrating
entanglement between distant quantum memories (realized with quantum dots),
which in turn is a milestone in the roadmap for building a functional quantum
repeater. We also place this experimental work in context by providing an
overview of quantum repeaters, their potential uses, and the challenges in
implementing them.Comment: 51 pages. Expanded version of a chapter to appear in "Engineering the
Atom-Photon Interaction" (Springer-Verlag, 2015; eds. A. Predojevic and M. W.
Mitchell
Quantum Teleportation from a Propagating Photon to a Solid-State Spin Qubit
The realization of a quantum interface between a propagating photon used for
transmission of quantum information, and a stationary qubit used for storage
and manipulation, has long been an outstanding goal in quantum information
science. A method for implementing such an interface between dissimilar qubits
is quantum teleportation, which has attracted considerable interest not only as
a versatile quantum-state-transfer method but also as a quantum computational
primitive. Here, we experimentally demonstrate transfer of quantum information
carried by a photonic qubit to a quantum dot spin qubit using quantum
teleportation. In our experiment, a single photon in a superposition state of
two colors -- a photonic qubit is generated using selective resonant excitation
of a neutral quantum dot. We achieve an unprecedented degree of
indistinguishability of single photons from different quantum dots by using
local electric and magnetic field control. To teleport a photonic qubit, we
generate an entangled spin-photon state in a second quantum dot located 5
meters away from the first and interfere the photons from the two dots in a
Hong-Ou-Mandel set-up. A coincidence detection at the output of the
interferometer heralds successful teleportation, which we verify by measuring
the resulting spin state after its coherence time is prolonged by an optical
spin-echo pulse sequence. The demonstration of successful inter-conversion of
photonic and semiconductor spin qubits constitute a major step towards the
realization of on-chip quantum networks based on semiconductor nano-structures.Comment: 12 pages, 3 figures, Comments welcom
Entanglement transfer from electron spins to photons in spin light-emitting diodes containing quantum dots
We show that electron recombination using positively charged excitons in
single quantum dots provides an efficient method to transfer entanglement from
electron spins onto photon polarizations. We propose a scheme for the
production of entangled four-photon states of GHZ type. From the GHZ state, two
fully entangled photons can be obtained by a measurement of two photons in the
linear polarization basis, even for quantum dots with observable fine structure
splitting for neutral excitons and significant exciton spin decoherence.
Because of the interplay of quantum mechanical selection rules and
interference, maximally entangled electron pairs are converted into maximally
entangled photon pairs with unity fidelity for a continuous set of observation
directions. We describe the dynamics of the conversion process using a
master-equation approach and show that the implementation of our scheme is
feasible with current experimental techniques.Comment: 5 pages, 2 figures. v2: Extended scheme, revised version. v3: Minor
additions and extended title, published versio
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