arXiv subjects

Yu Guo

Publications and source records attributed to Yu Guo.

At least 235 records · Page 13Linked to original sources

arXiv2017

Achieving robust and high-fidelity quantum control via spectral phase optimization

Achieving high-fidelity control of quantum systems is of fundamental importance in physics, chemistry and quantum information sciences. However, the successful implementation of a high-fidelity quantum control scheme also requires robustness against control field fluctuations. Here, we demonstrate a robust optimization method for control of quantum systems by optimizing the spectral phase of an ultrafast laser pulse, which is accomplished in the framework of frequency domain quantum optimal control theory. By incorporating a filtering function of frequency into the optimization algorithm, our numerical simulations in an abstract two-level quantum system as well as in a three-level atomic rubidium show that the optimization procedure can be enforced to search optimal solutions while achieving remarkable robustness against the control field fluctuations, providing an efficient approach to optimize the spectral phase of the ultrafast laser pulse to achieve a desired final quantum state of the system.

quant-ph↗

arXiv2017

Discordlike correlation of bipartite coherence

Quantum discord has been studied extensively as a measure of non-classical correlations which includes entanglement as a subset. Although it is well known that non-zero discord can exist without entanglement, the origin of quantum discord is not well understood as compared to entanglement, which manifests itself more simply as inseparable higher dimensional quantum superposition. In this paper we establish the discordlike correlation of bipartite coherence and then compare it to quantum discord. Consequently, we show that the minimum of the discordlike correlation of coherence coincides with the original quantum discord. This demonstrates quantum discord as the irreducible correlated bipartite coherence. In addition, the discordlike correlated coherence is shown to admit the postulates of the quantum resource theory (QRT), although the original quantum discord is not a "good" candidate under the QRT. We also find that the relative entropy measure induced from the discordlike coherence is a well-defined coherence measure for bipartite states.

quant-ph↗

arXiv2017

Unified view of monogamy relations for different entanglement measures

A particularly interesting feature of nonrelativistic quantum mechanics is the monogamy laws of entanglement. Although the monogamy relation has been explored extensively in the last decade, it is still not clear to what extent a given entanglement measure is monogamous. We give here a conjecture on the amount of entanglement contained in the reduced states by observing all the known related results at first. Consequently, we propose the monogamy power of an entanglement measure and the polygamy power for its dual quantity, the assisted entanglement, and show that both the monogamy power and the polygamy power exist in any multipartite systems with any dimension, from which we formalize exactly for the first time when an entanglement measure and an assisted entanglement obey the monogamy relation and the polygamy relation respectively in a unified way. In addition, we show that any entanglement measure violates the polygamy relation, which is misstated in some recent papers. Only the existence of monogamy power is conditioned on the conjecture, all other results are strictly proved.

quant-ph↗

arXiv2017

Bounds on skew information and local quantum uncertainty for state conversion

We establish strict upper bounds on local quantum uncertainty (LQU) and skew information associated with state conversion via certain quantum channels. Specifically, we obtain a bound on the achievable LQU for bipartite channels whose Kraus operators commute with nondegenerate von Neumann measurements on the first subsystem, and this LQU bound is expressed in terms of the skew information for the first subsystem. Furthermore, we establish a bound on the skew information of one subsystem obtained from any initial bipartite state subject to any quantum steering channel, and this bound is expressed in terms of the LQU for the initial joint-system state. Our two claims show that state conversion has fundamental limitations relating LQU with skew information.

quant-ph↗

arXiv2016

PT-symmetric spectral singularity and negative frequency resonance

Vacuum consists of a bath of balanced and symmetric positive and negative frequency fluctuations. Media in relative motion or accelerated observers can break this symmetry and preferentially amplify negative frequency modes as in Quantum Cherenkov radiation and Unruh radiation. Here, we show the existence of a universal negative frequency-momentum mirror symmetry in the relativistic Lorentzian transformation for electromagnetic waves. We show the connection of our discovered symmetry to parity-time (PT) symmetry in moving media and the resulting spectral singularity in vacuum fluctuation related effects. We prove that this spectral singularity can occur in the case of two metallic plates in relative motion interacting through positive and negative frequency plasmonic fluctuations (negative frequency resonance). Our work paves the way for understanding the role of PT-symmetric spectral singularities in amplifying fluctuations and motivates the search for PT-symmetry in novel photonic systems.

physics.optics↗

arXiv2016

Directed tunneling of a prescribed number of dipolar bosons in shaken triple-well potentials

We propose a scheme for precise control of tunneling dynamics of dipolar bosons in shaken triple-well potentials. In the high-frequency regimes and under the resonance conditions, we have analytically and numerically demonstrated that we can transport a priori prescribed number of dipolar bosons along different pathways and different directions by adjusting the driving parameters. These results extend the previous many-body selective coherent destruction of tunneling (CDT) schemes for nondipolar bosons in double-well potentials[Phys. Rev. Lett. 103, 133002 (2009); Phys. Rev. A 86, 044102 (2012)], thus offering an efficient way to design the long-range coherent quantum transportation.

quant-ph↗

arXiv2016

Constructing UMEB from maximally entangled basis

A new way of constructing unextendible maximally entangled basis (UMEB) from maximally entangled basis (MEB) is proposed. Consequently, it is shown that if there is an $N$-member UMEB in $\mathbb{C}^d\otimes \mathbb{C}^d$, then there exists a $(qd)^2-q(d^2-N)$-member UMEB in $\mathbb{C}^{qd}\otimes \mathbb{C}^{qd}$ for any $q\in\mathbb{N}$. This improves the results in [Phys. Rev. A 90, 034301(2014)], which shows that there exists a $(qd)^2-(d^2-N)$-member UMEB in $\mathbb{C}^{qd}\otimes \mathbb{C}^{qd}$ provided that an $N$-member UMEB exsits in $\mathbb{C}^d\otimes \mathbb{C}^d$. In addition, a very easy way of constructing UMEB in $\mathbb{C}^d\otimes \mathbb{C}^{d'}$ with $d<d'$ is presented, which promotes and covers all the previous related work.

quant-ph↗

arXiv2016

Universal Zero Conductivity Condition for Optical Absorption

Harnessing information and energy from light within a nanoscale mode volume is a fundamental challenge for nanophotonic applications ranging from solar photovoltaics to single photon detectors. Here, we show the existence of a universal condition in materials that sheds light on fundamental limits of electromagnetic to matter energy conversion (transduction). We show that the upper limit of absorption rate (transduction rate) in any nanoscale absorber converting light to matter degrees of freedom is revealed by the zero of optical conductivity at complex frequencies ($σ(ω^\prime + iω^{\prime\prime})= 0$). We trace the origin of this universal zero conductivity condition to causality requirements on any passive linear response function and propose an experiment of absorption resonances using plasmonic nanoparticles to experimentally verify this universal zero conductivity condition. Our work is widely applicable to linear systems across the electromagnetic spectrum and allows for systematic optimization of optical absorption in single photon detectors, solar cells, Coherent Perfect Absorbers and SPASERS.

physics.optics↗

arXiv2016

Conditions for coherence transformations under incoherent operations

We build the counterpart of the celebrated Nielsen's theorem for coherence manipulation in this paper. This offers an affirmative answer to the open question: whether, given two states $ρ$ and $σ$, either $ρ$ can be transformed into $σ$ or vice versa under incoherent operations [Phys. Rev. Lett. \textbf{113}, 140401(2014)]. As a consequence, we find that there exist essentially different types of coherence. Moreover, incoherent operations can be enhanced in the presence of certain coherent states. These extra states are coherent catalysts: they allow uncertain incoherent operations to be realized, without being consumed in any way. Our main result also sheds a new light on the construction of coherence measures.

quant-ph↗

arXiv2016

Non-commutativity measure of quantum discord

Quantum discord is a manifestation of quantum correlations due to non-commutativity rather than entanglement. Two measures of quantum discord by the amount of non-commutativity via the trace norm and the Hilbert-Schmidt norm respectively are proposed in this paper. These two measures can be calculated easily for any state with arbitrary dimension. It is shown by several examples that these measures can reflect the amount of the original quantum discord.

quant-ph↗

arXiv2015

Multipartite unextendible entangled basis

The unextendible entangled basis with any arbitrarily given Schmidt number $k$ (UEBk) in $\mathbb{C}^{d_1}\otimes\mathbb{C}^{d_2}$ is proposed in [Phys. Rev. A 90 (2014) 054303], $1<k\leq \min\{d_1,d_2\}$, which is a set of orthonormal entangled states with Schmidt number $k$ in a $d_1\otimes d_2$ system consisting of fewer than $d_1d_2$ vectors which have no additional entangled vectors with Schmidt number $k$ in the complementary space. In this paper, we extend it to multipartite case and a general way of constructing $(m+1)$-partite UEBk from $m$-partite UEBk is proposed ($m\geq 2$). Consequently, we show that there are infinitely many UEBks in $\mathbb{C}^{d_1}\otimes\mathbb{C}^{d_2}\otimes\cdots\otimes\mathbb{C}^{d_N}$ with any dimensions and any $N\geq3$.

quant-ph↗

arXiv2015

A generalization of Schmidt number for multipartite states

The Schmidt number is of crucial importance in characterizing the bipartite pure states. We explore and propose here a generalization of Schmidt number for states in multipartite systems. It is shown to be entanglement monotonic and valid for both pure and mixed states. In addition, the corresponding generalization of multipartite Schmidt coefficients is introduced. Our approach is applicable for systems with arbitrary number of parties and for arbitrary dimensions.

quant-ph↗

arXiv2015

Entangled bases with fixed Schmidt number

An entangled basis with fixed Schmidt number $k$ (EBk) is a set of orthonormal basis states with the same Schmidt number $k$ in a product Hilbert space $\mathbb{C}^d\otimes\mathbb{C}^{d'}$. It is a generalization of both the product basis and the maximally entangled basis. We show here that, for any $k\leq\min\{d,d'\}$, EBk exists in $\mathbb{C}^d\otimes\mathbb{C}^{d'}$ for any $d$ and $d'$. Consequently, general methods of constructing SEBk (EBk with the same Schmidt coefficients) and EBk (but not SEBk) are proposed. Moreover, we extend the concept of EBk to multipartite case and find out that the multipartite EBk can be constructed similarly.

quant-ph↗

arXiv2015

Flexible Online Repeated Measures Experiment

Online controlled experiments, now commonly known as A/B testing, are crucial to causal inference and data driven decision making in many internet based businesses. While a simple comparison between a treatment (the feature under test) and a control (often the current standard), provides a starting point to identify the cause of change in Key Performance Indicator (KPI), it is often insufficient, as the change we wish to detect may be small, and inherent variation contained in data may obscure movements in KPI. To have sufficient power to detect statistically significant changes in KPI, an experiment needs to engage a sufficiently large proportion of traffic to the site, and also last for a sufficiently long duration. This limits the number of candidate variations to be evaluated, and the speed new feature iterations. We introduce more sophisticated experimental designs, specifically the repeated measures design, including the crossover design and related variants, to increase KPI sensitivity with the same traffic size and duration of experiment. In this paper we present FORME (Flexible Online Repeated Measures Experiment), a flexible and scalable framework for these designs. We evaluate the theoretic basis, design considerations, practical guidelines and big data implementation. We compare FORME to an existing methodology called mixed effect model and demonstrate why FORME is more flexible and scalable. We present empirical results based on both simulation and real data. Our method is widely applicable to online experimentation to improve sensitivity in detecting movements in KPI, and increase experimentation capability.

stat.AP↗

arXiv2014

Thermal excitation of plasmons for near-field thermophotovoltaics

The traditional approaches of exciting plasmons consist of using electrons (eg: electron energy loss spectroscopy) or light (Kretchman and Otto geometry) while more recently plasmons have been excited even by single photons. A different approach: thermal excitation of a plasmon resonance at high temperatures using alternate plasmonic media was proposed by S. Molesky et.al., Opt. Exp. 21.101, A96-A110, (2013). Here, we show how the long-standing search for a high temperature narrow band near-field emitter for thermophotovoltaics can be fulfilled by high temperature plasmonics. We also describe how to control Wein's displacement law in the near-field using high temperature epsilon-near-zero metamaterials. Finally, we show that our work opens up an interesting direction of research for the field of slow light: thermal emission control.

physics.optics↗

arXiv2014

Giant non-equilibrium vacuum friction: Role of singular evanescent wave resonances in moving media

We recently reported on the existence of a singular resonance in moving media which arises due to perfect amplitude and phase balance of evanescent waves. We show here that the non-equilibrium vacuum friction (lateral Casimir-Lifshitz force) between moving plates separated by a finite gap is fundamentally dominated by this resonance. Our result is robust to losses and dispersion as well as polarization mixing which occurs in the relativistic limit.

physics.optics↗

arXiv2014

Unextendible entangled bases with fixed Schmidt number

The unextendible product basis (UPB) is generalized to the unextendible entangled basis with any arbitrarily given Schmidt number $k$ (UEBk) for any bipartite system $\mathbb{C}^d\otimes\mathbb{C}^{d'}$ ($2\leq k<d\leq d'$), which can also be regarded as a generalization of the unextendible maximally entangled basis (UMEB). A general way of constructing such a basis with arbitrary $d$ and $d'$ is proposed. Consequently, it is shown that there are at least $k-r$ (here $r=d$ mod $k$, or $r=d'$ mod $k$) sets of UEBk when $d$ or $d'$ is not the multiple of $k$, while there are at least $2(k-1)$ sets of UEBk when both $d$ and $d'$ are the multiples of $k$.

quant-ph↗

arXiv2014

Quantum correlation induced by the average distance between the reduced states

A new quantum correlation in terms of the average distance between the reduced state and the $i$-th output reduced states under local von Neumann measurements is proposed. It is shown that only the product states do not contain this quantum correlation and thus it is different from both the quantum discord (QD) [Phys. Rev. Lett. \textbf{88}, 017901 (2001)] and the measurement-induced nonlocality (MIN) [Phys. Rev. Lett. \textbf{106}, 120401(2011)]. For pure states, it is twice of the quantity MIN, and is smaller than QD and entanglement of formation (EOF). A general analytical formula is given and a lower bound for the two qubits case is obtained. Furthermore, we compare it with EOF and QD through the Werner state and the isotropic state respectively.

quant-ph↗