|Subject: Quantum speed limit time
Date: Mon, 02 Sep 2002 13:43:52 +0300
From: Dimi Chakalov <firstname.lastname@example.org>
To: Seth Lloyd <email@example.com>
CC: firstname.lastname@example.org, email@example.com,
Dear Dr. Lloyd,
May I ask you to shed some light on the basic premise of your article "The role of entanglement in dynamical evolution", quant-ph/0206001 [Ref. 1]. You and your co-authors wrote:
"We have shown that entanglement between different subsystems is an important resource to achieve the ultimate speed in dynamical evolution."
Q1: How would you reconcile your idea with the fact that these "subsystems" have no property at all [Ref. 2]?
Q2: What physical clock could possibly read a *finite* time interval pertaining to some "quantum state evolution" and hence "quantum speed limit time"?
To properly understand this question, please see
You also wrote:
"This work was funded by the ARDA, NRO, and by ARO under a MURI program."
Q3: How did you manage to convince the military to finance your work?
[Ref. 1] Vittorio Giovannetti, Seth Lloyd,
Lorenzo Maccone. The role of entanglement in dynamical evolution. Date
(revised v2): Fri, 30 Aug 2002 19:21:20 GMT,
[Ref. 2] GianCarlo Ghirardi, Luca Marinatto.
Entanglement and Properties.
"Up to this point we have confined our attention to quantum
systems considered as a whole. However the phenomenon of quantum entanglement
makes the situation much more puzzling when consideration is given to composite
quantum systems and one raises the problem of the properties of their constituents.
As we will see, in such a case it is very common to meet situations (most
of which arise as a consequence of the interactions between the constituents)
in which the constituents themselves do not possess *any property whatsoever*.
This is a new feature which compels us to face a quite peculiar state of
affairs: not only must one limit drastically the actual properties of physical
systems (being in any case true that the system as a whole always has some
properties), but one is forced also to accept that the parts of a composite
system can have no property at all. In this way the quantum picture of
the universe as an "unbroken whole", or as "undivided", emerges."
Subject: Quantum computing and Father
Dear Dr. Lloyd,
I wonder if you can declare in plan flat post-Victorian English the conditions under which you will acknowledge that quantum computing is impossible.
You've been speculating on "quantum computing" for many years, and have been enjoying financial support from various academic and military research institutions, such as the Cambridge-MIT Initiative, NSF, Hewlett-Packard, NEC, CMI, AFOSR, ARDA/ARO, DARPA, and RIKEN [Refs. 3 and 4]. If you are not doing metaphysics but science, you should be able to 'put your cards on the table', as Andrew Steane did,
I wonder if you and/or any of your colleagues have the guts to do the same, from your perspective. Some of your colleagues, such as Carlton M. Caves and Jonathan P. Dowling, have decided to keep quiet, in a very special way,
As to your latest paper [Ref. 4], it seems to me that you can "talk about properties of quantum systems at the dinner table" (Bob Griffiths) only along the lines of the old Tanzanian saying: "How do we know that Father Christmas has a beard? We know it, because snow falls when he shakes his beard."
We just don't know the transition from quantum to classical regime, and back. Please see (i) the problem of Lorentz-invariant non-locality
and (ii) the mythical "decoherence",
Also, since you claim that your definition of decoherence,
equation (5) in [Ref. 4], "is no longer equivalent
to the condition that the
As far as I can remember, five years ago Bob Griffiths quickly suggested a solution in the framework of his interpretation of QM, but it was somehow neglected by his prominent colleagues. Maybe you can do better.
You can read this email also at
Soon on CD ROM.
[Ref. 3] Seth Lloyd, The Computational
Universe: Quantum gravity from quantum computation, quant-ph/0501135 v1,
[Ref. 4] Seth Lloyd, Decoherent histories
and generalized measurements, quant-ph/0504155 v1,
"A set of histories is decoherent if the probabilities
assigned to later
"As with projective measurements, it is straightforward to test whether or not a system is decoherent with respect to a set of operations S. To check for decoherence, prepare two sets of systems in the state p . Then make the measurements corresponding to the A . On one set, make measurements corresponding to the effects in S, and on the other set omit these measurements. Compare whether the results of the remaining experiments have the same probabilities in both sets. If they do, then the system is decoherent. If they do not, then the system is coherent.