We propose a class of qubit networks that admit perfect transfer any quantum state in fixed period time. Unlike many other schemes for computation and communication, these do not require couplings to be switched on off. When restricted N-qubit spin identical couplings, we show 2 log_3 N is the maximal communication distance hypercube geometries. Moreover, if one allows but different between qubits then can achieved over arbitrarily long distances linear chain.

We propose a class of qubit networks that admit perfect state transfer any two-dimensional quantum in fixed period time. further show such can distribute arbitrary entangled states between two distant parties, and can, by using systems parallel, transmit the higher-dimensional across network. Unlike many other schemes for computation communication, these do not require couplings to be switched on off. When restricted $N$-qubit spin identical couplings, we...

In this paper, we present a new entanglement monotone for bipartite quantum states. Its definition is inspired by the so-called intrinsic information of classical cryptography and given halved minimum conditional mutual over all tripartite state extensions. We derive certain properties measure which call "squashed entanglement": it lower bound on formation an upper distillable entanglement. Furthermore, convex, additive tensor products, superadditive in general. Continuity only property our...

We propose a general method for studying properties of quantum channels acting on an n-partite system, whose action is invariant under permutations the subsystems. Our main result that, in order to prove that certain property holds arbitrary input, it sufficient consider case where input particular de Finetti-type state, i.e., state which consists n identical and independent copies (unknown) single subsystem. technique can be applied analysis information-theoretic problems. For example,...

Quantum computers can accurately compute ground state energies using phase estimation, but this requires a guiding that has significant overlap with the true state. For large molecules and extended materials, it becomes difficult to find states good for growing molecule sizes. Additionally, required number of qubits quantum gates may become prohibitively large. One approach dealing these challenges is use embedding method, which allows reduction one or multiple smaller cores embedded in...

Transfer of data in linear quantum registers can be significantly simplified with preengineered but not dynamically controlled interqubit couplings. We show how to implement a mirror inversion the state register each excitation subspace respect center register. Our construction is especially appealing as it requires no dynamical control over individual interactions. If, however, interactions available then operation performed on any substring qubits In this case, sequence inversions generate...

We study the computational complexity of $N$-representability problem in quantum chemistry. show that this is Merlin-Arthur complete, which generalization nondeterministic polynomial time complete. Our proof uses a simple mapping from spin systems to fermionic systems, as well convex optimization technique reduces finding ground states $N$ representability.

Quantum state tomography is the task of inferring a quantum system by appropriate measurements. Since frequency distributions outcomes any finite number measurements will generally deviate from their asymptotic limits, estimates computed standard methods do not in general coincide with true and, therefore, have no operational significance unless accuracy defined terms error bounds. Here we show that tomography, together an data analysis procedure, yields reliable and tight bounds, specified...

We consider the decomposition of arbitrary isometries into a sequence single-qubit and Controlled-NOT (C-NOT) gates. In many experimental architectures, C-NOT gate is relatively 'expensive' hence we aim to keep number these as low possible. derive theoretical lower bound on gates required decompose an isometry from m n qubits, give three explicit decompositions that achieve this up factor about two in leading order. also perform some bespoke optimizations for certain cases where are small....

Unraveling Entanglement is a curious property of some quantum mechanical systems, exploited in applications such as information processing. Walter et al. (p. 1205 ) used an algebraic geometry approach to represent the entanglement multiparticle system pure state geometric space whose axes are associated with properties individual particles. In that space, classes—collections entangled states can be transformed into each other—correspond different convex polytopes, making it possible...

The Quantum Reverse Shannon Theorem states that any quantum channel can be simulated by an unlimited amount of shared entanglement and classical communication equal to the channel's assisted capacity. In this paper, we provide a new proof theorem, which has previously been proved Bennett, Devetak, Harrow, Shor, Winter. Our clear structure being based on two recent information-theoretic results: one-shot State Merging Post-Selection Technique for channels.

We imagine an experiment on unknown quantum mechanical system in which the is prepared various ways and a range of measurements are performed. For each measurement $M$ preparation $\ensuremath{\rho}$ experimenter can determine, given enough time, probability outcome $a$: $p(a\ensuremath{\mid}M,\ensuremath{\rho})$. How large does Hilbert space have to be order allow us find density matrices operators that will reproduce distribution? In this paper, we prove simple lower bound for dimension...

This thesis presents a study of the structure bipartite quantum states. In first part, representation theory unitary and symmetric groups is used to analyse spectra particular, it shown how derive one-to-one relation between state its reduced states, Kronecker coefficients group. second focus lies on entanglement Drawing an analogy distillation secret-key agreement in classical cryptography, new measure, `squashed entanglement', introduced.

The Pauli exclusion principle is a constraint on the natural occupation numbers of fermionic states. It has been suspected since at least 1970s, and only proved very recently, that there multitude further constraints these numbers, generalizing principle. Here, we provide first analytic analysis physical relevance constraints. We compute for ground states family interacting fermions in harmonic potential. Intriguingly, find are almost, but not exactly, pinned to boundary allowed region...

A fundamental task in modern cryptography is the joint computation of a function which has two inputs, one from Alice and Bob, such that neither can learn more about other's input than what implied by value function. In this Letter, we show any quantum protocol for classical deterministic outputs result to both parties (two-sided computation) secure against cheating Bob be completely broken Alice. Whereas it known protocols cannot secure, our implies security party complete insecurity other....

We present a hierarchy of quantum many-body states among which many examples topological order can be identified by construction. define these in terms general, basis-independent framework tensor networks based on the algebraic setting finite-dimensional Hopf C*-algebras. At top we identify ground new lattice models extending Kitaev's double [Ann. Phys. 303, 2 (2003)10.1016/S0003-4916(02)00018-0]. For exhibit mechanism responsible for their non-zero entanglement entropy constructing an...

We study the quantumness of bipartite correlations by proposing a quantity that combines measure total correlations---mutual information---with notion broadcast copies---i.e., generally nonfactorized copies---of states. By analyzing how our increases with number copies, we are able to classify classical, separable, and entangled This motivates definition regularization mutual information, asymptotic minimal information per copy, which show have many properties an entanglement measure.