Bell inequality in an exactly soluble spin-1/2 XX chain displaying spin-Peierls transition

2014 ◽  
Vol 87 (12) ◽  
Author(s):  
Bai-Jun Chen ◽  
Zhao-Yu Sun ◽  
Hai-Lin Huang ◽  
Bo Wang
Keyword(s):  
Bell Inequality ◽  
Peierls Transition

scholarly journals Device-independent quantum key distribution with random key basis

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
René Schwonnek ◽  
Koon Tong Goh ◽  
Ignatius W. Primaatmaja ◽  
Ernest Y.-Z. Tan ◽  
Ramona Wolf ◽  
...  
Keyword(s):  
Quantum Key Distribution ◽  
Bell Inequality ◽  
Key Distribution ◽  
Theory And Practice ◽  
Information Theoretic ◽  
Information Theoretic Security ◽  
Experimental Parameters ◽  
Secret Keys ◽  
Simple Variant ◽  
First Time

AbstractDevice-independent quantum key distribution (DIQKD) is the art of using untrusted devices to distribute secret keys in an insecure network. It thus represents the ultimate form of cryptography, offering not only information-theoretic security against channel attacks, but also against attacks exploiting implementation loopholes. In recent years, much progress has been made towards realising the first DIQKD experiments, but current proposals are just out of reach of today’s loophole-free Bell experiments. Here, we significantly narrow the gap between the theory and practice of DIQKD with a simple variant of the original protocol based on the celebrated Clauser-Horne-Shimony-Holt (CHSH) Bell inequality. By using two randomly chosen key generating bases instead of one, we show that our protocol significantly improves over the original DIQKD protocol, enabling positive keys in the high noise regime for the first time. We also compute the finite-key security of the protocol for general attacks, showing that approximately 108–1010 measurement rounds are needed to achieve positive rates using state-of-the-art experimental parameters. Our proposed DIQKD protocol thus represents a highly promising path towards the first realisation of DIQKD in practice.

Theoretical evidence for the Peierls transition in NbO2

2021 ◽  
Vol 104 (3) ◽  
Author(s):  
Kathrin Kulmus ◽  
Sibylle Gemming ◽  
Michael Schreiber ◽  
Dimitar Pashov ◽  
Swagata Acharya
Keyword(s):  
Peierls Transition ◽  
Theoretical Evidence

scholarly journals Symmetrized persistency of Bell correlations for Dicke states and GHZ-based mixtures

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Marcin Wieśniak
Keyword(s):  
Communication Complexity ◽  
Quantum Communication ◽  
Bell Inequality ◽  
Bell Inequalities ◽  
Quantum Correlations ◽  
Complexity Reduction ◽  
Main Difficulty ◽  
Quantum Communication Complexity ◽  
Number Of Particles ◽  
Dicke States

AbstractQuantum correlations, in particular those, which enable to violate a Bell inequality, open a way to advantage in certain communication tasks. However, the main difficulty in harnessing quantumness is its fragility to, e.g, noise or loss of particles. We study the persistency of Bell correlations of GHZ based mixtures and Dicke states. For the former, we consider quantum communication complexity reduction (QCCR) scheme, and propose new Bell inequalities (BIs), which can be used in that scheme for higher persistency in the limit of large number of particles N. In case of Dicke states, we show that persistency can reach 0.482N, significantly more than reported in previous studies.

scholarly journals Trading Locality for Time: Certifiable Randomness from Low-Depth Circuits

2021 ◽  
Author(s):  
Matthew Coudron ◽  
Jalex Stark ◽  
Thomas Vidick
Keyword(s):  
Linear Time ◽  
Bell Inequality ◽  
Quantum Circuit ◽  
Constant Depth ◽  
Information Theoretic ◽  
Small Constant ◽  
Fundamental Information ◽  
Simple Quantum ◽  
Variation Distance ◽  
Noise Tolerant

AbstractThe generation of certifiable randomness is the most fundamental information-theoretic task that meaningfully separates quantum devices from their classical counterparts. We propose a protocol for exponential certified randomness expansion using a single quantum device. The protocol calls for the device to implement a simple quantum circuit of constant depth on a 2D lattice of qubits. The output of the circuit can be verified classically in linear time, and is guaranteed to contain a polynomial number of certified random bits assuming that the device used to generate the output operated using a (classical or quantum) circuit of sub-logarithmic depth. This assumption contrasts with the locality assumption used for randomness certification based on Bell inequality violation and more recent proposals for randomness certification based on computational assumptions. Furthermore, to demonstrate randomness generation it is sufficient for a device to sample from the ideal output distribution within constant statistical distance. Our procedure is inspired by recent work of Bravyi et al. (Science 362(6412):308–311, 2018), who introduced a relational problem that can be solved by a constant-depth quantum circuit, but provably cannot be solved by any classical circuit of sub-logarithmic depth. We develop the discovery of Bravyi et al. into a framework for robust randomness expansion. Our results lead to a new proposal for a demonstrated quantum advantage that has some advantages compared to existing proposals. First, our proposal does not rest on any complexity-theoretic conjectures, but relies on the physical assumption that the adversarial device being tested implements a circuit of sub-logarithmic depth. Second, success on our task can be easily verified in classical linear time. Finally, our task is more noise-tolerant than most other existing proposals that can only tolerate multiplicative error, or require additional conjectures from complexity theory; in contrast, we are able to allow a small constant additive error in total variation distance between the sampled and ideal distributions.

scholarly journals Coherently controlled quantum features in a coupled interferometric scheme

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Byoung S. Ham
Keyword(s):  
Optical Materials ◽  
Bell Inequality ◽  
Third Order ◽  
Deterministic Method ◽  
Photon Pairs ◽  
Wave Nature ◽  
Parametric Down Conversion ◽  
Pair Generation ◽  
Entangled Photon Pairs ◽  
Down Conversion

AbstractOver the last several decades, entangled photon pairs generated by spontaneous parametric down conversion processes in both second-order and third-order nonlinear optical materials have been intensively studied for various quantum features such as Bell inequality violation and anticorrelation. In an interferometric scheme, anticorrelation results from photon bunching based on randomness when entangled photon pairs coincidently impinge on a beam splitter. Compared with post-measurement-based probabilistic confirmation, a coherence version has been recently proposed using the wave nature of photons. Here, the origin of quantum features in a coupled interferometric scheme is investigated using pure coherence optics. In addition, a deterministic method of entangled photon-pair generation is proposed for on-demand coherence control of quantum processing.

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