This report gives a lower bound of entanglement cost for antisymmetric states of bipartite d-level systems to be log_2 (d/(d-1)) ebit (for d=3, E_c >= 0.585...). The paper quant-ph/0112131 claims that the value is equal to one ebit for d=3, since all of the eigenvalues of reduced matrix of any pure states living in N times tensor product of antisymmetric space is not greater than 2^(-N) thus the von Neumann entropy is not less than N, but the proof is not true. Hence whether the value is equal to or less than one ebit is not clear at this moment.
We have synthesized the anti-symmetric spin exchange interaction (ASI), which is also called the Dzyaloshinskii-Moriya interaction, in a superconducting circuit containing five superconducting qubits connected to a bus resonator, by periodically modulating the transition frequencies of the qubits with different modulation phases. This allows us to show the chiral spin dynamics in three-, four- and five-spin clusters. We also demonstrate a three-spin chiral logic gate and entangle up to five qubits in Greenberger-Horne-Zeilinger states. Our results pave the way for quantum simulation of magneti…
The entanglement dynamics of a laser-pumped two-level quantum dot pair is investigated in the steady-state. The closely spaced two-level emitters, embedded in a semiconductor substrate, interact with both the environmental vacuum modes of the electromagnetic field reservoir as well as with the lattice vibrational phonon thermostat. We have found that the entanglement among the pair's components is substantially enhanced due to presence of the phonon subsystem. The reason is phonon induced decay among the symmetrical and antisymmetrical two-qubit collective states and, consequently, the populat…
Minimal energy cost of thermodynamic information processes only with entanglement transfer
我们提出了最小的能量成本的测量和信息擦除，仅使用亥姆霍兹自由能和纠缠的形成。形成的纠缠以差分的形式出现，表示过程中存储器上的纠缠转移量;测量的代价由纠缠增益给出，而信息擦除的代价由可用纠缠的损失给出。将本函和Rev. E 88，042143（2013）放在一起，我们可以仅根据形成的纠缠来描述第二定律的违反和恢复;信息过程热力学对传统热力学第二定律的超额功和信息过程的总代价都由形成纠缠给出，且前者小于或等于后者。
What is the energy cost of extracting entanglement from complex quantum systems? In other words, given a state of a quantum system, how much energy does it cost to extract m EPR pairs? This is an important question, particularly for quantum field theories where the vacuum is generally highly entangled. Here we build a theory to understand the energy cost of entanglement extraction. First, we apply it to a toy model, and then we define the entanglement temperature, which relates the energy cost to the amount of extracted entanglement. Next, we give a physical argument to find the energy cost of…
We first investigate the one-shot static entanglement cost to simulate a bipartite quantum channel under the set of non-entangling channels. The lower bound on the static entanglement cost is given by the generalized robustness of the target channel as well as the robust-generating power of the channel, which implies that the cost necessary to generate a bipartite quantum channel might not be retrievable in general. Next, we conceive a set of quantum channels that extends the set of non-entangling channels. We find out that the one-shot static entanglement cost under the extended set of channe…
In this paper we pose the question of how one can quantify the amount of entanglement necessary to create a given steering assemblage, when the original state and measurements are unknown. To do this, we extend the concepts of entanglement cost and entanglement of formation to steering assemblages, and show how to upper bound them with semidefinite programming. We prove that the entanglement of formation for assemblages is not generally continuous and not a flat roof extension; and use numerical analysis to illustrate these properties. Finally, we discuss the consequences of these results for …
We prove that there is a trade-off relation between the entanglement cost and the number of rounds of communication, for two distant parties to accomplish a bidirectional quantum information task by local operations and classical communication (LOCC). We consider an implementation of a class of two-qubit controlled-unitary gate by LOCC assisted by shared entanglement, in an information theoretical scenario of asymptotically many input pairs and vanishingly small error. We prove the trade-off relation by showing that one ebit of entanglement per pair is necessary to be consumed for implementing…
对于一对空间分离的粒子的某些联合测量，我们问需要多少纠缠才能精确地进行测量。对于一类具有部分纠缠本征态的两量子比特正交测量，给出了纠缠代价的上下界。上界是基于D. Berry [Phys.Rev.A75，032349（2007）]。基于测量的纠缠生产能力的下限意味着，对于我们考虑的几乎所有测量，执行测量所需的纠缠严格大于其本征态的平均纠缠。另一方面，我们证明了对于在所有局部泡利操作下不变的d x d维的任何完整测量，测量的成本正好等于与结果相关的状态的平均纠缠。
The Schmidt number is an entanglement measure whose logarithm quantifies the zero-error entanglement cost of generating a given quantum state using local operations and classical communication (LOCC). %However, the Schmidt number is a notoriously difficult quantity to compute, and its relationship to other entanglement measures is largely unknown. In this paper we show that the Schmidt number is highly non-multiplicative in the sense that for any integer $n$, there exists states whose Schmidt number remains constant when taking $n$ copies of the given state. These states also provide a rare in…
Classical communication and entanglement cost in preparing a class of multi-qubit states
最近，几种类似的方案[J.Opt.B4（2002）380; Phys.Lett. A 316（2003）159; Phys. Lett. A 355（2006）285; Phys. Lett. A 336（2005）317]提出了一种远程制备一类多比特态（即$α|0 ... 0>+β|1... 1>$）的方法。在本文中，通过应用受控非（CNOT）门，一个新的简单的协议，提出了远程准备这类状态。与以往的协议相比，该协议的经典通信开销和所需的量子纠缠都有显著的降低。此外，我们的协议中识别某些量子态的难度也降低了。因此，我们的协议更经济和可行。
