Faster-than-light communication is possible via quantum entanglement in an EPR experiment if one can overcome nature's "quantum modesty" and gain knowledge concerning the quantum state of a single photon. Using a special EPR source that produces precisely timed doublets of EPR photons (biphotons), I show how one can gain additional information about the photon's polarization state--information not accessible using the conventional one-photon-at-a-time EPR setup. Using the Hong-Ou-Mandel effect that describes how two identical photons combine at a neutral beamsplitter (NBS), I show how Bob can obtain enough polarization information about his B photons to unambiguously ascertain the polarization basis of Alice's distant measurement device which she has deployed to measure her A photons. I am proposing, in short, that EPR + HOM = FTL. Version 2 concludes with a refutation of its FTL claim due to Lev Vaidman.
Faster-than-light communication is possible via quantum entanglement in an EPR experiment if one can overcome nature's "quantum modesty" and gain knowledge concerning the quantum state of a single photon. Using a special EPR source that produces precisely timed doublets of EPR photons (biphotons), I show how one can gain additional information about the photon's polarization state--information not accessible using the conventional one-photon-at-a-time EPR setup. Using the Hong-Ou-Mandel effect that describes how two identical photons combine at a neutral beamsplitter (NBS), I show how Bob can obtain enough polarization information about his B photons to unambiguously ascertain the polarization basis of Alice's distant measurement device which she has deployed to measure her A photons. I am proposing, in short, that EPR + HOM = FTL. Version 2 concludes with a refutation of its FTL claim due to Lev Vaidman.
Abstract The Hong−Ou−Mandel (HOM) effect was long believed to be a two-photon interference phenomenon. It describes the fact that two indistinguishable photons mixed at a beam splitter will bunch together to one of the two output modes. Considering the two single-photon emitters such as trapped ions, we explore a hidden scenario of the HOM effect, where entanglement can be generated between the two ions when a single photon is detected by one of the detectors. A second photon emitted by the entangled photon sources will be subsequently detected by the same detector. However, we can also control the fate of the second photon by manipulating the entangled state. Instead of two-photon interference, the phase of the entangled state is responsible for the photon’s path in our proposal. Toward a feasible experimental realization, we conduct a quantum jump simulation on the system to show its robustness against experimental errors.
Present understanding of non-possibility of Quantum communication rests on analysis of possibility of signalling within a Quantum system. Is it possible to achieve signalling by a setup where the system is changed from one to another where the act of change serves as the signal and the change in the measurement probabilities would be detected and deciphered at the receiver end? A proposal is made where a variant of Delayed Choice Quantum Eraser experiment setup of Kim et al is used to achieve the same. The setup is also designed such that the speed of communication can be faster than light. NonLocality and Quantum communication Nonlocality is a feature of Quantum Mechanics that has been firmly established through experiments [Aspect et al, 1981] and well accepted now. Entangled particles separated by a distance still are part of one entity and when that entity changes state by a measurement in one part of it the change happens instantaneously across the domain the entity pervades. Is it possible to use this instantaneous state change to transmit information across at high speeds, faster than light (FTL)? This issue has been dealt with from the time the Einstein raised the EPR paradox [Einstein et al,1935] and has been claimed to be impossible and shown to be so by Peres, [Peres and Tenko, 2004] through the no-communication theorem which shows that any amount of signalling by Alice through measurements done at one end of the quantum system would not be sufficient for Bob to detect and decipher at the other end of the system. However the discussions in literature (as above) always deal with information transfer within a stable quantum system by making measurements at one end and analysing the possibility of detecting it at the other end. Peres and Tenko analyse a Quantum System S of mixed-state where Alice and Bob make measurements at their ends of the system. The authors derive the probability that Bob’s outcome is ν as
Schrödinger held that a local quantum system has some objectively real quantum state and no other (hidden) properties. He therefore took the Einstein-Podolsky-Rosen (EPR) phenomenon, which he generalized and called `steering', to require nonlocal wavefunction collapse. Because this would entail faster-than-light (FTL) information transmission, he doubted that it would be seen experimentally. Here we report a demonstration of EPR steering with entangled photon pairs that puts--in Schrödinger's interpretation--a non-zero lower bound on the amount of FTL information transmission. We develop a family of n-setting loss-tolerant EPR-steering inequalities allowing for a size-d classical message sent from Alice's laboratory to Bob's. For the case n=3 and d=2 (one bit) we observe a statistically significant violation. Our experiment closes the efficiency and locality loopholes, and we address the freedom-of-choice loophole by using quantum random number generators to independently choose Alice's and Bob's measurement basis settings. To close the efficiency and locality loopholes simultaneously, we introduce methods for quickly switching between three mutually unbiased measurement bases and for accurately characterizing the efficiency of detectors. From the space-time arrangement of our experiment, we can conclude that if the mechanism for the observed bipartite correlations is that Alice's measurement induces wave-function collapse of Bob's particle, then more than one bit of information must travel from Alice to Bob at more than three times the speed of light.
Abstract In Quantum Mechanics, two particles are entangled if their physical states depend on one another's so that if we find one of them in state A, for example, we will be sure that the other is in state B. However, until the state of a quantum particle is measured, it will be in a superposition of states, being in neither one nor the other until then, so when an entangled particle is measured, its pair also assumes a state instantly and regardless of how far away it is from the other particle at that time. As promising as it could be to use this fact for instantaneous communication, Quantum Mechanics seems to claim this is impossible, as no method ever invented to do this has worked until today. What we demonstrate here theoretically is that with a protocol and simple optical devices, two people who share polarized entangled pairs of photons can send information to each other faster than light. If this model of communication proves to be experimentally functional, we will have a contradiction to Einstein's theories of relativity, and otherwise, we will have Quantum Mechanics predicting something that does not happen in real life. This result, therefore, shows there is something fundamental about the universe we do not know yet. One of these theories must be mistaken and both deal with fundamental aspects of reality, such as the dynamics of space and time, and the particles that almost all matter around us are made of. Besides, this result is of great relevance also because it has immediate applications in several areas if the model works experimentally, as in space exploration and security, since it will allow the creation of non-interceptable instantaneous communication technologies.
We show how the property of dualism, which can exist in the entanglement of identical particles, can be tested in the usual photonic Bell measurement apparatus with minor modifications. Two different sets of coincidence measurements on the same experimental setup consisting of a Hong-Ou-Mandel interferometer demonstrate how the same two-photon state can emerge entangled in the polarization or the momentum degree of freedom depending on the dynamical variables used for labeling the particles. Our experiment demonstrates how the same source can be used as both a polarization entangled state as well as a dichotomic momentum entangled state shared between distant users Alice and Bob in accordance with which sets of detectors they access. When the particles become distinguishable by letting the information about one of the variables be imprinted in yet another (possibly inaccessible) system or degree of freedom, the feature of dualism is expected to vanish. We verify this feature by polarization decoherence (polarization information in the environment) or arrival time difference, which both respectively destroy one of the dual forms of entanglement.
Hong–Ou–Mandel (HOM) interference is a quantum optics laboratory experiment that has recently become more accessible to undergraduate students. The experiment consists of two identical photons simultaneously entering a nonpolarizing beamsplitter, where the photon wavefunctions interfere. As a result, the photon pair exits from the same beamsplitter output, whereas classically, the two photons are equally likely to exit from the two different outputs. This effect is demonstrated by observation of a dip in coincidence counts measured between the two beamsplitter outputs. Due to the precision needed to achieve photon indistinguishability, the setup and alignment of this experiment is often considered to be too difficult and time consuming to be appropriate for the undergraduate instructional laboratory. Here, we present an alternative optical-fiber-based apparatus that gives a consistently reproducible experiment. In our approach, quantum interference occurs within a fused-fiber coupler, instead of within a traditional beamsplitter. We use a commercially available fiber-coupled biphoton source that requires minimal alignment and increases the interference coherence length. In addition, our biphoton source provides direct temperature-based control of the frequency degeneracy of the photon pairs, allowing students to investigate physical properties of HOM interference such as coherence length and interference visibility. Through use of standard optomechanical parts, combined with the commercially available fiber-integrated biphoton source, our apparatus is positioned midway between a completely built-from-scratch and a pre-aligned setup, making it ideal for the advanced instructional laboratory.