|Subject: Fishing in murky waters: Quantum computing
Date: Mon, 17 Jun 2002 21:28:22 +0300
From: "Dimiter G. Chakalov" <email@example.com>
CC: firstname.lastname@example.org, email@example.com,
Dear Dr. Milburn,
In your recent article "Quantum Technology: The Second Quantum Revolution", quant-ph/0206091 [Ref. 1], you and your co-author Jonathan Dowling wrote:
"As yet there is no dedicated effort in quantum technology as such, and the field itself has only just begun to define itself as a discipline. However we are convinced that as these experiments move form the lab to the market place the emergence of a new discipline of quantum technology or quantum engineering is almost certain, and it is not at all too early to ask where the wise money should be invested."
Surely not in "quantum computing",
To make a quantum computer, you have to keep the entangled state 'alive and kicking' for a finite time interval, as read with you clock,
NB: The target word in your article [Ref. 1] is "simultaneously". It seems to me that this is a privilege of the human brain only, for which two modes of time may apply,
If I'm on the right track, forget about "error-free quantum computing".
You also wrote: "The quantum cryptographic keys distributed in this fashion are provably immune to attack -- guaranteed by the Heisenberg Uncertainty Principle."
There is no guarantee here, simply because no one knows the nature of quantum reality,
To understand the postulates in QM introduced 'by hand', which make QM a highly successful calculation tool eluding any intuitive understanding,
I believe we need new physics,
That is, quantum gravity,
Since we don't have it yet, I think it is quite premature to include the dream of "quantum computing" in the basket of all potentially viable quantum technologies.
I regret that this email will be automatically deleted by your co-author Jonathan Dowling,
and by Carlton Caves,
I won't benefit from their professional criticism, regrettably.
If possible, may I ask you to forward my email to your co-author, since he acknowledged "additional support" from the Office of Naval Research, the Advanced Research and Development Activity, the National Security Agency, and the Defense Advanced Research Projects Agency [Ref. 1]. I think the time has come to put his cards on the table. The sooner, the better.
I will appreciate your questions and critical comments, as well as those by your colleagues included in CC: and BCC: lists.
Please do not hesitate.
You can read this email also at
[Ref. 1] Jonathan P. Dowling, Gerard J.
Milburn. Quantum Technology: The Second Quantum Revolution. Thu, 13 Jun
2002 21:25:08 GMT,
"The hallmark of this Second Quantum Revolution is the
realization that we humans are no longer passive observers of the quantum
world that Nature has given us.
"Thus, although quantum mechanics as a science has matured
completely, quantum engineering as a technology is now emerging on
its own right. It is just a matter of being in the right place at the right
time to take full advantage of these new development.
"The objective of quantum technology is to deliver useful devices and processes that are based on quantum principles which include:
. Quantisation (quantum size effect); the allowed energies of a tightly confined system of particles are restricted to a discrete set.
· Uncertainty principle; for every perfectly specified quantum state there is always at least one measurement, the results of which are completely certain, and simultaneously at least one measurement for which the results are largely random.
· Quantum Superposition; if an event can be realized in two or more indistinguishable ways, the state of the system is a superposition of each way simultaneously.
· Entanglement: the superposition principle applied to certain nonlocal correlations, if a correlation can be realized in two or more indistinguishable ways, the state of the system is a superposition of all such correlations simultaneously.
· Decoherence: what happens to quantum superpositions
when an attempt is made to distinguish previously indistinguishable ways
an event can be realized. It renders superpositions of probability amplitudes
into superpositions of classical probabilities. Decoherence has no analogue
in classical physics.
"Building a quantum computer is the greatest challenge
for a future quantum technology, requiring the ability to manipulate quantum-entangled
states for millions of sub-components. Such a technology will necessarily
incorporate the previous three quantum applications for readout (quantum
metrology), error correction (quantum control), and interconnects (quantum
"From 1980 until 1994, the theory and experiments on nonlocal
quantum correlations remained an obscure branch of the Foundations of Quantum
Mechanics. However, all that changed with two breakthroughs in 1994, when
two critical events took place that began the quantum information revolution.
The first was the experimental demonstration, by a group at the British
Defence Evaluation and Research Agency (DERA), that nonlocal photon correlations
could be used to make an unbreakable quantum cryptographic key distribution
system over 4 km of optical fiber . The second was the theoretical
exposition by Shor that a quantum computer, by harnessing these delicate
nonlocal quantum entanglements, could provide an exponential speed up in
computational power for some intractable numerical problems . Thus,
in 1994 the world learned that quantum entanglement was important technological
tool and not just a curiosity.
"While quantum computing is still in its infancy, quantum
cryptography is here and now. (...) Los Alamos National Lab (LANL) is currently
working on such a free space system in the group of Richard Hughes. The
quantum cryptographic keys distributed in this fashion are provably immune
to attack -- guaranteed by the Heisenberg Uncertainty Principle. This result,
when coupled with the threat quantum computers now pose to existing public
key systems, gives a new quantum way of transmitting secure data, in a
fashion that is proven to be unbreakable -- even by a quantum computer
"In addition, quantum error correction codes are being
developed all over the world to ensure error-free operation of a quantum
computer, once the technology is in place .
"Compared to some of the other ideas in coherent quantum
electronics, discussed above, the SQUID technology is already well developed.
Still, there is much to be done, including the possible application to
quantum computers. However, there is a serious roadblock that has yet to
"Ultimately, molecular electronics may be able to utilise
the self assembly that characterises biological systems, paving the way
for a nanotechnology that mimics biological systems, a bio-mimetic nanotechnology.
"As mentioned above there has been considerable progress
in harnessing superconducting quantum degrees of freedom for quantum information
processing, and the first all solid-state qubit has been demonstrated in
such a device . A solid state quantum computer is probably the most
daunting quantum technological challenge of all and will require huge advances
in almost all the areas of quantum technology we have discussed.
"Commercial applications are even further away for many
of the technologies, although there are some promising beginnings (quantum
cryptography for example). As yet there is no dedicated effort in quantum
technology as such, and the field itself has only just begun to define
itself as a discipline. However we are convinced that as these experiments
move form the lab to the market place the emergence of a new discipline
of quantum technology or quantum engineering is almost certain, and it
is not at all too early to ask where the wise money should be invested.
"One of the authors (JPD) would like
to thank the Office of Naval Research, the Advanced Research and Development
Activity, the National Security Agency, and the Defense Advanced Research
Projects Agency for additional support."
I'm certainly optimistic about quantum technologies, although I haven't read your book. I don't work in this field, for obvious reasons,
but I try to follow closely the publications relevant to atom laser coherence, such as [Ref. 1], and phase coherence in general [Ref. 2]. I believe the control of phase coherence is in reach of the human brain. You don't have to elevate stone blocks to build pyramids:-)
No need to reply, I just wanted to to say something positive, but it's still 'fishing in murky waters'.
[Ref. 1] L.K. Thomsen, H.M. Wiseman.
Atom laser coherence and its control via feedback.
See Sec. IV "Reducing the linewidth via feedback", and
Sec. V "Summary", p. 12: "Basically, by feeding back the results of a QND
measurement of the number fluctuations to control the condensate energy,
it is possible to compensate for the linewidth caused by the frequency
fluctuations. The very number-phase correlation created by the collisions
is utilized to cancel their effect."
[Ref. 2] William A. Tiller. A
White Paper on The Law of Cause and Effect.
"(b) Coherence: To illustrate this principle, let us consider the case of a typical home-use 60 watt light bulb (~1 watt/cm3). It provides some illumination but not a lot of illumination. This is primarily because the emitted photons destructively interfere with each other so that most of the bulb's potential effectiveness is destroyed. However, if we could somehow take the same number of photons emitted by the light bulb per second and orchestrate their emission to be in phase with each other, then we would have constructive interference between these photons (a laser) and now the energy density of the surface of the light bulb would be thousands to millions of times larger than that emitted by the surface of the sun (~6000 watts/cm2). This illustrates the unutilized potential in the present light bulb. Perhaps the best example of the development of coherent energy emissions from humans comes from studies of QiGong masters . They appear to emit beams of infra red radiation (~1 to 4. 5 microns) from their palms that have healing benefits."
 W. A. Tiller, Science and Human Transformation: Subtle Energies, Intentionality and Consciousness (Pavior Publishing, Walnut Creek, CA, 1997).
This "mumbling" led to the discovery of the cohesion energy (cf. G. Jordan Maclay, Heidi Fearn, and Peter W. Milonni, Of Some Theoretical Significance: Implications of Casimir Effects, quant-ph/0105002). See also:
Milonni, Controlling the speed of light pulses, J. Phys. B: At. Mol. Opt. Phys.
35 (2002) R31-R56; pdf file from
See Sec 6, Propagation of energy, p. R48: "In considering the velocity vE
of energy transport it is imperative to recognize the simple fact that part of
the energy density is stored for a finite time in the propagation medium."
Following Niels Bohr, I mumbled something about the Holon here. See also:
J. Maclay and R.L. Forward, "A Gedanken spacecraft that operates using the quantum vacuum (Dynamic Casimir effect)," Foundations of Physics (to be published March issue 2004); pdf file from here.