SciRate Comments

Comment on 0806.3982 by toner

Paper Id: 0806.3982
Paper Title: Quantum Multi Prover Interactive Proofs with Communicating Provers
Authors: Michael Ben-Or, Avinatan Hassidim, Haran Pilpel

toner said: This paper defines and characterizes a new form of quantum multi-prover interactive proof system. The authors consider a quantum verifier who can interact with multiple unentangled quantum provers. The twist is that the provers are allowed to exchange unlimited amounts of classical communication. Even so, the authors show that such a proof system can still recognize languages in NEXP. This is a wonderful result: the model is novel, the outcome is surprising, and there are some nice ideas used to devise the protocol.

The result probably also has implications for quantum information processing. There are a number of situations where one would like to find the optimal protocol for some task using LOCC (local operations with classical communication), e.g., LOCC state discrimination, entanglement distillation. The sentiment in the community is that these problems are difficult, and the result in this paper is a first indication as to why. I'm not aware of earlier work about the classical complexity of finding an optimal LOCC protocol.

The main idea is start with classical 2-prover proof system for NEXP and to modify it so that the verifier asks the questions from the classical proof system in superposition with fake questions, the answers of which he doesn't actually care about. To gain classical information about what the questions are, a prover would have to decohere the superposition, and the verifer can detect this.

Comment on 0806.2962 by matt.hastings

Paper Id: 0806.2962
Paper Title: Entropic bounds for the quantum marginal problem
Authors: Tobias J. Osborne

matt.hastings said: This paper is worth reading just to see the bound Eq. (2) on the number of solutions to the quantum marginal problem. The calculation is just a few lines and very clean.

Comment on 0806.1660 by QuantumMoxie

Paper Id: 0806.1660
Paper Title: Uncertainty relations in terms of Tsallis entropy
Authors: Grzegorz Wilk, Zbigniew Wlodarczyk

QuantumMoxie said: I need to read this more fully, but if this is correct it might be very useful in understanding the quantum-classical boundary.

Comment on 0806.0615 by pak

Paper Id: 0806.0615
Paper Title: Nanoengineering of a Negative-Index Binary-Staircase Lens for the Optics Regime
Authors: B. D. F. Casse, R. Banyal, W. T. Lu, Y. J. Huang, S. Selvarasah, M. Dokmeci, S. Sridhar

pak said: concave lens + surface corrugations = convex lens

Comment on 0806.0086 by jimh

Paper Id: 0806.0086
Paper Title: Long distance quantum key distribution without decoy state
Authors: Shi-Hai Sun, Cheng-Zu Li

jimh said: As far as I can tell, the authors make an assumption that the channel acts as a beamsplitter. In particular, the transmission probability of an n-photon pulse is given by $\eta_n = 1 - (1-\eta)^n$, where $\eta$ is the transmission probability of a single photon.

The whole point of decoy states is to be able to counter attacks such as photon-number-splitting, where an adversary may block single photon pulses and split off a photon from multi-photon pulses, which are let through otherwise undisturbed, in order to gain partial or full information on the sifted bits. If we assume that an eavesdropper has no such control over the quantum channel, then certainly decoy states are no longer needed to achieve security, but this is neither a good assumption against a sophisticated adversary nor is the analysis in such a case new.

Comment on 0806.0273 by pak

Paper Id: 0806.0273
Paper Title: "Bubbles in Society": The Example of the United States Apollo Program
Authors: Monika Gisler, Didier Sornette

pak said: interesting ... but where's the mathematical analysis?

Comment on 0805.3640 by pak

Paper Id: 0805.3640
Paper Title: A sign error in the Minkowski space-time plot and its consequences
Authors: J. H. Field

pak said: a valiant attempt... but let down by an odd def of the Lorentz transform (see eq. (2.3,2.4)) and various other mistakes
(e.g eq. (3.7,3.8) isn't a rotation)

Comment on 0805.1632 by QuantumMoxie

Paper Id: 0805.1632
Paper Title: Separability and Entanglement of Quantum States Based on Covariance Matrices
Authors: Ming Li, Shao-Ming Fei, Zhi-Xi Wang

QuantumMoxie said: Might prove useful for studying mixed quantum states in gravitational fields.

Comment on 0805.1728 by QuantumMoxie

Paper Id: 0805.1728
Paper Title: Hidden-variable simulation of quantum measurements
Authors: Borivoje Dakic, Milovan Suvakov, Tomasz Paterek, Caslav Brukner

QuantumMoxie said: Is this the first actual simulation of Rob's model (or generalized version of said model) or has someone put his model to the test before?

Comment on 0708.2992 by breic

Paper Id: 0708.2992
Paper Title: Quantum private queries
Authors: Vittorio Giovannetti, Seth Lloyd, Lorenzo Maccone

breic said: Summary:
The authors describe a scheme where Alice can make quantum queries to a database Bob. If Bob tries to cheat to learn what Alice queried, then she catches him with constant probability.

Let D_j be the jth entry in the database. Fix entry 0 of the database to be D_0 = 0. To query j > 0, Alice sends |j> and |0>+|j> in random order to Bob. She waits for Bob's response before she sends the second one. Bob is supposed to respond respectively with |j, D_j> or |0,0> + |j,D_j>. Alice can clearly get D_j. Intuitively, Bob can't learn j because he doesn't know whether he is seeing |j> or |0>+|j>. If he measures the latter, then he will collapse the superposition, which Alice can detect.

They don't actually give a security proof in any detail, but say that a full proof will be forthcoming.