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Tunneling Transfer Protocol in a Quantum Dot Chain Immune to Inhomogeneity

100%
Korzekwa K., Machnikowski P.
Acta Physica Polonica A
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2011
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vol. 120
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issue 5
859-861
EN
We propose a quantum dot implementation of a quantum state transfer channel. The proposed channel consists of N vertically stacked quantum dots with the nearest neighbor tunnel coupling, placed in an axial electric field. We show that the system supports high-fidelity transfer of the state of a terminal dot both by free evolution and by adiabatic transfer. The protocol is to a large extent insensitive to inhomogeneity of the energy parameters of the dots and requires only a global electric field.
2
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Bose-Einstein Condensates in Optical Lattices

80%
Wasilewski W., Trippenbach M., Rzążewski K.
Acta Physica Polonica A
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2002
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vol. 101
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issue 1
47-60
EN
We study an ultracold dilute gas of bosonic atoms in an optical lattice induced by intersecting laser beams. As a first approximation we neglect confining potential and atom-atom interactions. In this case the Gross-Pitaevskij equation reduces to simple Mathieu equation. Upon choosing periodic boundary conditions this problem has well known periodic solution. This simple picture allows to demonstrate localization of the wave packet and formation of the band structure. We calculate spectrum of the excited states as a function of the strength of modulating potential and using a standard adiabaticity criterion we predict the most efficient way to ramp up optical lattice, without higher state excitation. Finally, we discuss the influence of the atom-atom interaction (nonlinearity) on the adiabaticity of the process.
3
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Enhancing the W State Fusion Process With a Toffoli Gate and a CNOT Gate via One-Way Quantum Computation and Linear Optics

80%
Diker F., Ozaydin F., Arik M.
Acta Physica Polonica A
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2015
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vol. 127
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issue 4
1189-1190
EN
Creation of large-scale W state quantum networks is a key step for realization of various quantum information tasks. Regarding the photonics technology, a simple optical setup was proposed for the fusion of two W states. Recently it was shown that via a single Fredkin gate, this basic so-called "fusion setup" can be enhanced. However the main problem was that the probability of success of realization of Fredkin gate with linear optics is too low. In this work, we show that the same enhancement can be made possible via one Toffoli and one CNOT gate, instead of a Fredkin gate. Not only the probability of success of the combination of these two gates is much higher, than that of a single Fredkin gate via linear optics, but also there is another method for implementing our setup with current photonics technology, almost with a unity success probability: A hybrid circuit consisting of a Toffoli gate which can be implemented via one-way quantum computation on a weighted graph state of 8 qubits with a unity success probability and a linear optical CNOT gate which has a success probability close to unity. Therefore the preparation of polarization based encoded multi particle entangled W states of arbitrary sizes becomes considerably more efficient.
4
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Quantum Cryptography with Macroscopic Photon-Number-Correlated Light

80%
Raymer M., Funk A.
|
EN
We describe a new scheme for performing quantum key distribution. We present two physical implementations for the quantum key distribution system. The first implementation uses a type-II optical-parametric amplifier to generate the optical pulses which contain the key information. The second implementation uses correlated semiconductor emitters to generate the optical pulses.
5
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On Mixed States Entanglement and Quantum Communication: Aspects of Quantum Channels Theory

80%
Horodecki P.
Acta Physica Polonica A
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2002
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vol. 101
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issue 3
399-424
EN
Basic aspects of quantum communication based on quantum channels theory are reviewed together with suitable examples. The key notion of quantum channel capacity is discussed. The role of mixed states entanglement as a practical tool in quantum channels theory is explained in detail. Application of recent results on non-positive partial transpose bound entanglement conjecture to binding entanglement channels shows that validity of the conjecture for some states implies nonadditivity of two-way quantum channel capacity. Some aspects of robustness of entanglement in context of positive maps theory are also discussed.
6
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Translating Concepts of State Transfer to Spin-1 Chains

80%
Wieśniak M., Dutta A., Ryu J.
Acta Physica Polonica A
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2015
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vol. 128
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issue 1
3-5
EN
State transfer is a well-known routine for various systems of spins-1/2. Still, it is not well studied for chains of spins of larger magnitudes. In this contribution we argue that while perfect state transfer may seem unnatural in spin-1 systems, it is still feasible for arrays of V-type three-level atoms. Tomography of such 1D array is also shown to be possible by acting on one atom from such an array.
7
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On entanglement distillation and quantum error correction for unknown states and channels

61%
Horodecki P.
Open Physics
|
2003
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vol. 1
|
issue 4
695-707
EN
We consider the problem of invariance of distillable entanglement D and quantum capacities Q under erasure of information about single copy of quantum state or channel respectively. We argue that any 2 ⊗N two-way distillable state is still two-way distillable after erasure of single copy information. For some known distillation protocols the obtained two-way distillation rate is the same as if Alice and Bob knew the state from the very beginning. The isomorphism between quantum states and quantum channels is also investigated. In particular it is pointed out that any transmission rate down the channel is equal to distillation rate with formal LOCC-like superoperator that uses in general nonphysical Alice actions. This allows to we prove that if given channel Λ has nonzero capacity (Q → or Q ⟺) then the corresponding quantum state ϱ(Λ) has nonzero distillable entanglement (D → or D ⟺). Follwoing the latter arguments are provided that any channel mapping single qubit into N level system allows for reliable two-way transmission after erasure of information about single copy. Some open problems are discussed.
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