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We consider the problem of reversing quantum dynamics, with the goal of preserving an initial state's quantum entanglement or classical correlation with a reference system. We exhibit an approximate… (More)

- Howard Barnum, Emanuel Knill, Michael Nielsen
- IEEE Trans. Information Theory
- 2000

For the discrete memoryless quantum channel, we show the equivalence of two different notions of quantum channel capacity: that which uses the entanglement fidelity as its criterion for success in… (More)

We present a new characterization of quantum theory in terms of simple physical principles that is different from previous ones in two important respects: first, it only refers to properties of… (More)

- Howard Barnum, Claude Crépeau, Daniel Gottesman, Adam D. Smith, Alain Tapp
- The 43rd Annual IEEE Symposium on Foundations of…
- 2001

Authentication is a well-studied area of classical cryptography: a sender A and a receiver B sharing a classical secret key want to exchange a classical message with the guarantee that the message… (More)

For finite-dimensional bipartite quantum systems, we find the exact size of the largest balls, in spectral ${l}_{p}$ norms for $1l~pl~\ensuremath{\infty},$ of separable (unentangled) matrices around… (More)

Noisy quantum channels may be used in many information-carrying applications. We show that different applications may result in different channel capacities. Upper bounds on several of these… (More)

We reformulate the notion of quantum query complexity in terms of inequalities and equations for a set of positive matrices, which we view as a quantum analogue of a decision tree. Using the new… (More)

- Howard Barnum, Jonathan Barrett, +5 authors Robin Niklas Wilke
- 2012

- Howard Barnum
- 1998

I introduce rate-distortion theory for quantum coding, and derive a lower bound, involving the coherent information, on the rate at which qubits must be used to encode a quantum source with a given… (More)

We show that for an m-partite quantum system, there is a ball of radius 2{sup -(m/2-1)} in Frobenius norm, centered at the identity matrix, of separable (unentangled) positive semidefinite matrices.… (More)