1,181 research outputs found
Hybrid entanglement for quantum communication
A dissertation submitted to the Faculty of Science
in partial fulfillment of the requirements for the Degree of
Master of Science
School of Physics
University of Witwatersrand
November 1, 2017The generation and detection of entangled photons is a topic of interest in quantum
communication. With current state-of-the-art methods it is possible to manipulate
any degree of freedom (DoF) of photons, e.g, polarisation, transverse momentum,
orbital angular momentum and energy. Furthermore, it is possible to combine these
DoF to realise hybrid entanglement { entanglement between the DoF of photons. In
this dissertation we focus on hybrid entanglement between photon states of coupled
orbital angular momentum and polarisation.
We engineer hybrid-entanglement using geometric phase control between spatially
separated photons produced from spontaneous parametric down conversion.
We present a new type of quantum eraser that does not rely on physical path interference.
We show that in principle any other degree of freedom can be used and
demonstrate this e ectively through polarisation control.
The use of high dimensional hybrid photon states in quantum communication,
particularly in quantum cryptography, is still in its infancy. Here we tailor photon
states that are coupled in their polarisation and spatial DoF (orbital angular momentum)
to realise high dimensional encoding alphabets. We show how photons entangled
in their internal DoF can be generated and deterministically detected. We exploit
them in a demonstration of a high dimensional quantum key distribution protocol
and show that our scheme generates secure keys at high rates.MT 201
A novel two-party semiquantum key distribution protocol based on GHZ-like states
In this paper, we propose a novel two-party semiquantum key distribution
(SQKD) protocol by only employing one kind of GHZ-like state. The proposed SQKD
protocol can create a private key shared between one quantum party with
unlimited quantum abilities and one classical party with limited quantum
abilities without the existence of a third party. The proposed SQKD protocol
doesn't need the Hadamard gate or quantum entanglement swapping. Detailed
security analysis turns out that the proposed SQKD protocol can resist various
famous attacks from an outside eavesdropper, such as the Trojan horse attacks,
the entangle-measure attack, the double CNOT attacks, the measure-resend attack
and the intercept-resend attack.Comment: 15 pages, 2 figures, 1 tabl
Roadmap on structured waves
Structured waves are ubiquitous for all areas of wave physics, both classical
and quantum, where the wavefields are inhomogeneous and cannot be approximated
by a single plane wave. Even the interference of two plane waves, or a single
inhomogeneous (evanescent) wave, provides a number of nontrivial phenomena and
additional functionalities as compared to a single plane wave. Complex
wavefields with inhomogeneities in the amplitude, phase, and polarization,
including topological structures and singularities, underpin modern nanooptics
and photonics, yet they are equally important, e.g., for quantum matter waves,
acoustics, water waves, etc. Structured waves are crucial in optical and
electron microscopy, wave propagation and scattering, imaging, communications,
quantum optics, topological and non-Hermitian wave systems, quantum
condensed-matter systems, optomechanics, plasmonics and metamaterials, optical
and acoustic manipulation, and so forth. This Roadmap is written collectively
by prominent researchers and aims to survey the role of structured waves in
various areas of wave physics. Providing background, current research, and
anticipating future developments, it will be of interest to a wide
cross-disciplinary audience.Comment: 110 pages, many figure
Test of mutually unbiased bases for six-dimensional photonic quantum systems
In quantum information, complementarity of quantum mechanical observables
plays a key role. If a system resides in an eigenstate of an observable, the
probability distribution for the values of a complementary observable is flat.
The eigenstates of these two observables form a pair of mutually unbiased bases
(MUBs). More generally, a set of MUBs consists of bases that are all pairwise
unbiased. Except for specific dimensions of the Hilbert space, the maximal sets
of MUBs are unknown in general. Even for a dimension as low as six, the
identification of a maximal set of MUBs remains an open problem, although there
is strong numerical evidence that no more than three simultaneous MUBs do
exist. Here, by exploiting a newly developed holographic technique, we
implement and test different sets of three MUBs for a single photon
six-dimensional quantum state (a qusix), encoded either in a hybrid
polarization-orbital angular momentum or a pure orbital angular momentum
Hilbert space. A close agreement is observed between theory and experiments.
Our results can find applications in state tomography, quantitative
wave-particle duality, quantum key distribution and tests on complementarity
and logical indeterminacy.Comment: 8 pages, 4 figure
Multi-photon entanglement and interferometry
Multi-photon interference reveals strictly non-classical phenomena. Its
applications range from fundamental tests of quantum mechanics to photonic
quantum information processing, where a significant fraction of key experiments
achieved so far comes from multi-photon state manipulation. We review the
progress, both theoretical and experimental, of this rapidly advancing
research. The emphasis is given to the creation of photonic entanglement of
various forms, tests of the completeness of quantum mechanics (in particular,
violations of local realism), quantum information protocols for quantum
communication (e.g., quantum teleportation, entanglement purification and
quantum repeater), and quantum computation with linear optics. We shall limit
the scope of our review to "few photon" phenomena involving measurements of
discrete observables.Comment: 71 pages, 38 figures; updated version accepted by Rev. Mod. Phy
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