Quantum fisher information of a 3 x 3 bound entangled state and its relation with geometric discord

Recent studies on quantum Fisher information (QFI) have been focused mostly on qubit systems within the context of how entanglement helps surpassing the classical limit of separable states and the limit that a given entangled system can achieve for parameter estimation. However, there are only a few works on bound entangled systems. In this work, we study the QFI of a system of the smallest dimension that bound entanglement can be observed: A bipartite quantum system of two particles of three-levels each. An interesting property of this state is that depending only on a parameter, the state can be separable, bound entangled or free entangled. We show that QFI exhibits a smooth and continues increase with respect to this parameter throughout the transition from separable to bound entangled and from bound entangled to free entangled regions. We show that in any region, this state is not useful for sub-shot noise interferometry. We also relate the QFI of this state with its geometric discord and show how these two properties exhibit a similar behavior throughout this transition.Publisher's VersionAuthor Post Prin

Self-localized soliton solutions of the nonlinear quantum harmonic oscillator

We analyze the existences, properties and stabilities of the self-localized solutions of the nonlinear quantum harmonic oscillator (NQHO) using spectral renormalization method (SRM). We show that self-localized single and dual soliton solutions of the NQHO do exist. Additionally we report that single and dual soliton solutions satisfy the necessary Vakhitov and Kolokolov slope condition, at least for the parameter ranges considered. Additionally, we investigate the stability characteristics of the single and dual soliton solutions using a split-step Fourier scheme. We show that single and dual soliton solutions are pulsating during time stepping. We discuss our findings and comment on our results.Publisher's Versio

Quantum Zeno repeaters

Quantum repeaters pave the way for long-distance quantum communications and quantum Internet, and the idea of quantum repeaters is based on entanglement swapping which requires the implementation of controlled quantum gates. Frequently measuring a quantum system affects its dynamics which is known as the quantum Zeno effect (QZE). Beyond slowing down its evolution, QZE can be used to control the dynamics of a quantum system by introducing a carefully designed set of operations between measurements. Here, we propose an entanglement swapping protocol based on QZE, which achieves almost unit fidelity. Implementation of our protocol requires only simple frequent threshold measurements and single particle rotations. We extend the proposed entanglement swapping protocol to a series of repeater stations for constructing quantum Zeno repeaters which also achieve almost unit fidelity regardless of the number of repeaters. Requiring no controlled gates, our proposal reduces the quantum circuit complexity of quantum repeaters. Our work has potential to contribute to long distance quantum communications and quantum computing via quantum Zeno effect.Publisher's VersionQ2WOS:000859184900014PMID: 3609703

Quantum metrology: Surpassing the shot-noise limit with Dzyaloshinskii-Moriya interaction

PubMed ID: 26549409Entanglement is at the heart of quantum technologies such as quantum information and quantum metrology. Providing larger quantum Fisher information (QFI), entangled systems can be better resources than separable systems in quantum metrology. However the effects on the entanglement dynamics such as decoherence usually decrease the QFI considerably. On the other hand, Dzyaloshinskii-Moriya (DM) interaction has been shown to excite entanglement. Since an increase in entanglement does not imply an increase in QFI, and also there are cases where QFI decreases as entanglement increases, it is interesting to study the influence of DM interaction on quantum metrology. In this work, we study the QFI of thermal entanglement of two-qubit and three-qubit Heisenberg models with respect to SU(2) rotations. We show that even at high temperatures, DM interaction excites QFI of both ferromagnetic and antiferromagnetic models. We also show that QFI of the ferromagnetic model of two qubits can surpass the shot-noise limit of the separable states, while QFI of the antiferromagnetic model in consideration can only approach to the shot-noise limit. Our results open new insights in quantum metrology with Heisenberg models.This work was funded by Isik University Scientific Research Fund, Grant Number: BAP-14A101. FO thanks S. Tekinay, for her continuous supportPublisher's Versio

Enhancing the W state fusion process with a toffoli gate and a CNOT gate via one-way quantum computation and linear optics

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.Publisher's Versio

Analysis of entanglement measures and LOCC maximized quantum fisher information of general two qubit systems

PubMed ID: 24957694Entanglement has been studied extensively for unveiling the mysteries of non-classical correlations between quantum systems. In the bipartite case, there are well known measures for quantifying entanglement such as concurrence, relative entropy of entanglement (REE) and negativity, which cannot be increased via local operations. It was found that for sets of non-maximally entangled states of two qubits, comparing these entanglement measures may lead to different entanglement orderings of the states. On the other hand, although it is not an entanglement measure and not monotonic under local operations, due to its ability of detecting multipartite entanglement, quantum Fisher information (QFI) has recently received an intense attraction generally with entanglement in the focus. In this work, we revisit the state ordering problem of general two qubit states. Generating a thousand random quantum states and performing an optimization based on local general rotations of each qubit, we calculate the maximal QFI for each state. We analyze the maximized QFI in comparison with concurrence, REE and negativity and obtain new state orderings. We show that there are pairs of states having equal maximized QFI but different values for concurrence, REE and negativity and vice versa.Publisher's Versio

Preparing multipartite entangled spin qubits via pauli spin blockade

PubMed ID: 32103078Preparing large-scale multi-partite entangled states of quantum bits in each physical form such as photons, atoms or electrons for each specific application area is a fundamental issue in quantum science and technologies. Here, we propose a setup based on Pauli spin blockade (PSB) for the preparation of large-scale W states of electrons in a double quantum dot (DQD). Within the proposed scheme, two W states of n and m electrons respectively can be fused by allowing each W state to transfer a single electron to each quantum dot. The presence or absence of PSB then determines whether the two states have fused or not, leading to the creation of a W state of n + m − 2 electrons in the successful case. Contrary to previous works based on quantum dots or nitrogen-vacancy centers in diamond, our proposal does not require any photon assistance. Therefore the ‘complex’ integration and tuning of an optical cavity is not a necessary prerequisite. We also show how to improve the success rate in our setup. Because requirements are based on currently available technology and well-known sensing techniques, our scheme can directly contribute to the advances in quantum technologies and, in particular in solid state systems.Ministry of Education, Culture, Sports, Science and TechnologyS.B. acknowledges Japanese Government MEXT scholarship. S.B. also thanks to Mizuki Kobayashi and Raisei Mizoguchi for helpful discussions. F.O. acknowledges the Personal Research Fund of Tokyo International University. T.K. acknowledges JSPS KAKENHI Grant Number: JP18K18996, JST CREST (JPMJ CR1675) and MEXT Quantum Leap Flagship Program (MEXT Q-LEAP) Grant Number JPMXS0118069228.Publisher's Versio

Prisoners’ dilemma in a spatially separated system based on spin–photon interactions

This research was funded by the Personal Research Fund of Tokyo International University.Having access to ideal quantum mechanical resources, the prisoners’ dilemma can be ceased. Here, we propose a distributed quantum circuit to allow spatially separated prisoners to play the prisoners’ dilemma game. Decomposing the circuit into controlled-Z and single-qubit gates only, we design a corresponding spin–photon-interaction-based physical setup within the reach of current technology. In our setup, spins are considered to be the players’ logical qubits, which can be realized via nitrogen-vacancy centers in diamond or quantum dots coupled to optical cavities, and the game is played via a flying photon realizing logic operations by interacting with the spatially separated optical cavities to which the spin qubits are coupled. We also analyze the effect of the imperfect realization of two-qubit gates on the game, and discuss the revival of the dilemma and the emergence of new Nash equilibria.Publisher's VersionQ3WOS:00085696110000

Behavior of quantum fisher information of bell pairs under decoherence channels

Quantum Fisher information has recently been an essential tool for analyzing the phase sensitivity of the quantum states in various quantum tasks, requiring high precision, such as quantum clock synchronization, positioning and many applications which include quantum interferometers. Due to the interactions with the environment, all quantum systems are subject to various decoherence effects. Therefore the research on quantum Fisher information under decoherence has been recently attracting more attention. In this work, analyzing the quantum Fisher information, we study the phase sensitivity of bipartite quantum correlations, in particular four Bell pairs amplitude damping channels. For a specific Bell state we arrive at similar results of Greenberger-Horne-Zeilinger (GHZ) states (as expected). For the other three Bell states, we present our results which point the interesting behavior of quantum Fisher information with respect to the decoherence rate. We also find the regions where the quantum Fisher information exhibits discontinuities.Publisher's Versio

Quantum fisher information of bipartitions of W states

We study the quantum Fisher information (QFI) of W states and W-like states under decoherence. In particular, we find that on the contrary to amplitude damping and depolarizing decoherence, a W-like state of 3 qubits obtained by discarding 1 qubit of a genuine W state of 4 qubits is more robust than a genuine W state of 3 qubits under amplitude amplifying and phase damping decoherence.This work was funded by Isik University Scientific Research Fund, Grant No. BAP-14A101Publisher's Versio