"Recently CCNY physics graduate Demetrios Kalamidas proposed a clever
    faster-than-light signaling scheme [DK1] which survived peer review and
    was recently published in Journal of the Optical Society of America. Kalamidas's FTL scheme has generated much discussion and controversy which I will attempt to summarize in this brief review."
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    • Jack Sarfatti Nick Herbert continues: "I wish to emphasize that I am not a member of the quantum-optics community nor am I proficient in boson algebra. I am however familiar with devising and refuting FTL communication schemes [1]. I would appreciate comments, corrections and additions to this review.
      Kalamidas's scheme is based on a path-uncertain pair of photons shared by
      Alice and Bob. Whenever Bob's photon path is certain, then so is Alice's, and
      no path interference can occur at Alice's detectors. But if Bob erases which-path information at his detectors, so the argument goes, Alice's which-path information is also (instantly!) erased and interference ensues at Alice's detectors.
      By turning his quantum eraser on and off, Bob can send an FTL signal
      to Alice in the form of patterns of interference or no-interference.
      The beauty of Kalamidas's scheme resides in his original method of which-path
      erasure. When Bob's path info is certain, one path contain a single photon
      and the other path is empty, symbolized by |10> or |01>."
    • Jack Sarfatti "Kalamidas proposes to erase which-path info by mixing into each path a kind of light whose photon number is uncertain. The source of this number-uncertain light is a coherent state |A> which is mixed with Bob's photons via a weakly reflecting beam splitter ( r --> 0) where A is adjusted so that a "weak
      coherent state" |rA> = |0> + rA |1> blends with whatever is in Bob's path. [2] This scheme leads to 5 possible outputs |01>, |01>, |11>, |02> and |20>. For four of these outputs, the path Bob's photon took is not erased, but whenever Bob's counters read |11>, which path the photon took is uncertain and erasure ensues. Using this scheme, Kalamidas can demonstrate apparent FTL signaling from Bob to Alice."
    • Jack Sarfatti "Once I heard of this scheme, I publicized it on my blog [NH1] and hastened to refute it. I was able to invent a simpler path-erasure scheme using "Gray light" |U> instead of a coherent state (where |U> = x|0> + y|1>) which was easy to refute[NH2]. But I could not refute Kalamidas's original scheme.
      Instead of refuting DK's scheme, I actually enhanced it by showing that if he
      strengthened his "weak coherent state" by expanding it to higher powers of
      (rA), the intensity of his FTL signal would actually increase [NH3]. At about
      this same time I wrote the theme song for an opera celebrating DK's quixotic
      quest [NH4] and issued a second blog post [NH5] publicly challenging the
      physics community to refute DK's audacious scheme. The first physicist to take up the challenge was John Howell at the University of Rochester who produced a general refutation of FTL schemes using photon- mixing of the Kalamidas type [JH1]. John's proof used Displaced Fock States (DFS) as Bob's counter outputs and suggested moreover that Kalamidas had erred by using Photon-added Coherent States (PACS) instead of DFS.
      "Everyone knows" that DFS are the correct output states for this kind of experiment, Howell insisted. This has been shown both theoretically and by experiment, for instance here [L&B] and here [W/MS/al]. Kalamidas could not see where his derivation was flawed, but it was clear that his states were of the PACS type. So if DFS was correct, he was prepared to reluctantly admit defeat. However Martin Suda from Austrian Institute of Technology came to the rescue with a simple proof, that at this particular stage of the beam-splitter algebra, both PACS and DFS were correct states [MS1], an astonishing result I call "the Martin Suda Paradox".
    • Jack Sarfatti Nick continued: "Coincidently, GianCarlo Ghirardi had just published a review of past FTL signaling schemes [GCG1] and was drawn into the debate. Together with Raffaele Romano, Ghirardi produced a general refutation [G&R] based on "unitary operations." If the operations that Kalamidas performed on his photons were all unitary, then G & R showed that no FTL signaling would ensue.
      Then one of Kalamidas's former teachers and author of several lucid texts on
      quantum-optics, Christopher Gerry, composed a general refutation [CG/etal]
      based on PACS, the same states Kalamidas had used in his scheme. John
      Howell, at about the same time, published a slightly different refutation [JH2]
      also based on PACS.
    • Jack Sarfatti "One might imagine that, confronted with so many general refutations from all sides, that Kalamidas would cave in and admit defeat. But a funny thing happened on the way to the refutation.
      Despite all the general proofs that his scheme was impossible, no one had
      been able to find a mistake in Kalamidas's math nor his physics. It was true
      that his scheme involved an APPROXIMATION but approximations are used
      all the time in physics. DK's "weak coherent state", for instance, is a veritable
      workhorse of quantum optics, is quite well-understood and appears in numerous experiments where it causes no paradoxical behavior. Kalamidas could cite considerable precedent for using this approximation. One of the reviewers quite rightly pointed out that if the general proofs (which contain no approximations) said that DK's FTL scheme could not work, then that certainly spelled doom for all approximate schemes such as the one DK was proposing. To which DK boldly replied: since you are so certain--because of your general proofs--that I am wrong, then it should be "easy pickins" for you to discover my mistake. But no one has yet met this Kalamidas challenge."
    • Jack Sarfatti "There are two issues here 1. the PACS vs DFS issue and 2. the EXACT vs
      APPROXIMATION issue.
      General refutations using both the PACS and DFS formulations have been
      derived but the PACS APPROXIMATION scheme has not been refuted. It
      remains a mystery why this refutation has not occurred.
      To top things off, Martin Suda formulated a Kalamidas-like scheme using
      DFS APPROXIMATION instead of PACS [MS2]. Suda's new scheme, even
      though approximate, was easily refuted--all the FTL signaling terms obligingly
      summed to zero. However, Martin's nice refutation was spoiled by the
      presence of an ugly non-physical |00> term which no one could justify or
      What is the meaning of this impasse? Why can't Kalamidas's simple approximation be refuted when the unapproximated schemes are easily destroyed.
      Martin faintly suspects it has to do with the way the vacuum states |0> are
      treated in approximation schemes. I've always been confused whenever vacuum
      states appear in calculations mixed with "real states". Maybe Kalamidas's
      stubbornly unrefuted FTL scheme (which is certainly wrong, make no
      mistake) has something new and subtle to teach us about boson algebra."
      Nick Herbert (This email address is being protected from spambots. You need JavaScript enabled to view it.) June 5, 2013
    • Jack Sarfatti REFERENCES
      [1] Nick Herbert "Faster Than Light: Superluminal Loopholes in
      Physics" NAL (1989)<http://www.amazon.com/gp/product/
      - 4 -
      [2] A coherent state is conventionally written |alpha>, where "alpha"
      is a complex number. For typographical convenience, I write a
      coherent state as |A> where A is understood to be the upper-case
      Greek "alpha".
      [DK1] Demetrios Kalamidas "A Proposal for a Feasible Quantum-
      Optical Experiment to Test the Validity of the No-signaling
      Theorem" <http://lanl.arxiv.org/abs/1110.4629>--Kalamidas's
      original proposal in the physics arXiv.
      [NH1] Nick Herbert "The Kalamida Experiment (blog)" <http:/
      html>--Publicizing (#1) DK's FTL communication
      scheme; Confirmation of APPROX DK FTL Scheme
      [NH2] Nick Herbert "The Kalamidas Experiment (pdf)" <http:/
      /quantumtantra.com/KalamidasFINAL.pdf>--Refutation of FULL
      Gray-light version of DK FTL Scheme. (In these references "FULL"
      [NH3] Nick Herbert "Maximizing the Kalamidas Effect (pdf)" <http:/
      /quantumtantra.com/Kalamidas1.pdf>--Expanding & Confirming
      DK APPROX FTL Scheme to higher powers of rA.
      [NH4] Nick Herbert "Demetrios! The Opera (blog)" <http:/
      Demetrios! The Opera.
      [NH5] Nick Herbert (blog) "FTL Signaling Made Easy" <http:/
      html>--Publicizing (#2) APPROX DK FTL Signaling Scheme.
      [JH1] John Howell "Refutation of the Kalamidas's Signaling" (private
      communication) //Refutation of FULL DFS version of DK FTL Scheme
      - 5 -
      [W/MS/al] A. Windhager, Martin Suda et al "Quantum Interference
      between a Single-photon Fock State and a Coherent State" <http:/
      /arxiv.org/pdf/1009.1844.pdf> -- derivation of DFS output of a
      beamsplitter with input |A, 1>
      [L&B] AI Lvovski & SA Babichev "Synthesis and Tomographic
      Characterization of the Displaced Fock State" <http://lanl.arxiv.org/
      abs/quant-ph/0202163>--production and measurement of DFS at
      beam splitter output.
      [GCG1] GianCarlo Ghirardi "Entanglement, Non-locality,
      Superluminal Signaling and Cloning" <http://lanl.arxiv.org/pdf/
      1305.2305v1.pdf>--Refutation of several historical FTL signaling
      [G&R] GianCarlo Ghirardi & Raffaelle Romano "On a quite recent
      proposal of faster than light communication" (private
      communication)--General Refutation of all Full Unitary Systems.
      [CGetal] Christopher Gerry, VV, Ugur Güney & Mark Hillery
      "Comment on a superluminal signaling scheme" (private
      communication)--Refutation of FULL PACS version of DK FTL
      [MS1] "MARTIN SUDA PARADOX" (private communication)--"Martin
      Suda Paradox": Symmetry of PACS and DFS at BS output.
      [MS2] Martin Suda "Interferometry at the 50/50 BS" (private
      communication)--refutation of APPROX DFS version of DK FTL
      [JH2} John Howell "Full Calculation No Approximation" (private
      communication)//refutation of FULL PACS version of DK FTL