00508nas a2200169 4500008004100000245006400041210006300105260001400168300001200182490000800194100001600202700001800218700001800236700002200254700002500276856003700301 2022 eng d00aKramers' degeneracy for open systems in thermal equilibrium0 aKramers degeneracy for open systems in thermal equilibrium c3/10/2022 aL1211040 v1051 aLieu, Simon1 aMcGinley, Max1 aShtanko, Oles1 aCooper, Nigel, R.1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2105.0288801727nas a2200157 4500008004100000245004800041210004700089260001500136300001100151490000700162520129200169100001701461700001901478700001601497856005601513 2018 eng d00aKeyring models: an approach to steerability0 aKeyring models an approach to steerability c2018/01/02 a0221030 v593 a
If a measurement is made on one half of a bipartite system then, conditioned on the outcome, the other half has a new reduced state. If these reduced states defy classical explanation — that is, if shared randomness cannot produce these reduced states for all possible measurements — the bipartite state is said to be steerable. Determining which states are steerable is a challenging problem even for low dimensions. In the case of two-qubit systems a criterion is known for T-states (that is, those with maximally mixed marginals) under projective measurements. In the current work we introduce the concept of keyring models — a special class of local hidden state model. When the measurements made correspond to real projectors, these allow us to study steerability beyond T-states. Using keyring models, we completely solve the steering problem for real projective measurements when the state arises from mixing a pure two-qubit state with uniform noise. We also give a partial solution in the case when the uniform noise is replaced by independent depolarizing channels. Our results imply that Werner states, which are a special case of the previous states, are unsteerable under real projective measurements if and only if their efficiency is at most 2/π.
1 aMiller, Carl1 aColbeck, Roger1 aShi, Yaoyun uhttp://aip.scitation.org/doi/full/10.1063/1.500619901814nas a2200205 4500008004100000245007600041210006900117260001500186300001100201490000700212520120100219100001901420700002701439700001301466700002301479700002101502700002401523700002501547856003601572 2016 eng d00aKaleidoscope of quantum phases in a long-range interacting spin-1 chain0 aKaleidoscope of quantum phases in a longrange interacting spin1 c2016/05/11 a2051150 v933 aMotivated by recent trapped-ion quantum simulation experiments, we carry out a comprehensive study of the phase diagram of a spin-1 chain with XXZ-type interactions that decay as 1/rα, using a combination of finite and infinite-size DMRG calculations, spin-wave analysis, and field theory. In the absence of long-range interactions, varying the spin-coupling anisotropy leads to four distinct phases: a ferromagnetic Ising phase, a disordered XY phase, a topological Haldane phase, and an antiferromagnetic Ising phase. If long-range interactions are antiferromagnetic and thus frustrated, we find primarily a quantitative change of the phase boundaries. On the other hand, ferromagnetic (non-frustrated) long-range interactions qualitatively impact the entire phase diagram. Importantly, for α≲3, long-range interactions destroy the Haldane phase, break the conformal symmetry of the XY phase, give rise to a new phase that spontaneously breaks a U(1) continuous symmetry, and introduce an exotic tricritical point with no direct parallel in short-range interacting spin chains. We show that the main signatures of all five phases found could be observed experimentally in the near future. 1 aGong, Zhe-Xuan1 aMaghrebi, Mohammad, F.1 aHu, Anzi1 aFoss-Feig, Michael1 aRicherme, Philip1 aMonroe, Christopher1 aGorshkov, Alexey, V. uhttp://arxiv.org/abs/1510.0210801319nas a2200169 4500008004100000245004200041210004100083260001400124490000800138520086500146100001901011700001701030700002101047700002501068700001901093856003701112 2014 eng d00aKitaev chains with long-range pairing0 aKitaev chains with longrange pairing c2014/10/90 v1133 a We propose and analyze a generalization of the Kitaev chain for fermions with long-range $p$-wave pairing, which decays with distance as a power-law with exponent $\alpha$. Using the integrability of the model, we demonstrate the existence of two types of gapped regimes, where correlation functions decay exponentially at short range and algebraically at long range ($\alpha > 1$) or purely algebraically ($\alpha < 1$). Most interestingly, along the critical lines, long-range pairing is found to break conformal symmetry for sufficiently small $\alpha$. This is accompanied by a violation of the area law for the entanglement entropy in large parts of the phase diagram in the presence of a gap, and can be detected via the dynamics of entanglement following a quench. Some of these features may be relevant for current experiments with cold atomic ions. 1 aVodola, Davide1 aLepori, Luca1 aErcolessi, Elisa1 aGorshkov, Alexey, V.1 aPupillo, Guido uhttp://arxiv.org/abs/1405.5440v201632nas a2200157 4500008004100000245007100041210006900112260001500181300001600196490000800212520114600220100002501366700002601391700002001417856003701437 2013 eng d00aKitaev honeycomb and other exotic spin models with polar molecules0 aKitaev honeycomb and other exotic spin models with polar molecul c2013/01/01 a1908 - 19160 v1113 a We show that ultracold polar molecules pinned in an optical lattice can be used to access a variety of exotic spin models, including the Kitaev honeycomb model. Treating each molecule as a rigid rotor, we use DC electric and microwave fields to define superpositions of rotational levels as effective spin degrees of freedom, while dipole-dipole interactions give rise to interactions between the spins. In particular, we show that, with sufficient microwave control, the interaction between two spins can be written as a sum of five independently controllable Hamiltonian terms proportional to the five rank-2 spherical harmonics Y_{2,q}(theta,phi), where (theta,phi) are the spherical coordinates of the vector connecting the two molecules. To demonstrate the potential of this approach beyond the simplest examples studied in [S. R. Manmana et al., arXiv:1210.5518v2], we focus on the realization of the Kitaev honeycomb model, which can support exotic non-Abelian anyonic excitations. We also discuss the possibility of generating spin Hamiltonians with arbitrary spin S, including those exhibiting SU(N=2S+1) symmetry. 1 aGorshkov, Alexey, V.1 aHazzard, Kaden, R. A.1 aRey, Ana, Maria uhttp://arxiv.org/abs/1301.5636v1