A team of researchers from the Massachusetts Institute of Technology (MIT) and Northwestern University (NU) is developing a system for long-distance, high- delity qubit tele-portation. Such a system will be required if future quantum computers are to be linked together into a quantum Internet. This paper presents recent progress that the MIT/NU team has made, beginning with a review of the teleportation architecture and its loss-limited performance analysis.

Previously, we had proposed a gravitational wave detector that incorporates the white light cavity (WLC) effect using a compound cavity for signal recycling (CC-SR).Here, we first use an idealized model for the negative dispersion medium (NDM), and use the so-called Caves model for phase-insensitive linear amplifier to account for the quantum noise (QN) contributed by the NDM, in order to determine the upper bound of the enhancement in the sensitivity-bandwidth product. We calculate the quantum noise limited sensitivity curves for the CC-SR design, and find that the broadening of sensitivity predicted by the classical analysis is also present in these curves, but is somewhat reduced. Furthermore, we find that the curves always stay above the standard quantum limit (SQL). To circumvent this limitation, we modify the dispersion to compensate the non-linear phase variation produced by the opto-mechanical (OM) resonance effects. We find that the upper bound of the factor by which the sensitivitybandwidth product is increased, compared to the highest sensitivity result predicted by Bunanno and Chen [Phys. Rev. D 64, 042006 (2001)], is ~14. We also present a simpler scheme (WLC-SR) where a dispersion medium is inserted in the SR cavity. For this scheme, we found the upper bound of the enhancement factor to be ~18. We then consider an explicit system for realizing the NDM, which makes use of five energy levels in M-configuration to produce Gain, accompanied by Electromagnetically Induced Transparency (the GEIT system). For this explicit system, we employ the rigorous 2 approach based on Master Equation (ME) to compute the QN contributed by the NDM, thus enabling us to determine the enhancement in the sensitivity-bandwidth product definitively rather than the upper bound thereof. Specifically, we identify a set of parameters for which the sensitivity-bandwidth product is enhanced by a factor of 17.66.

We describe an enhanced rotation sensor involving an active helium-neon (HeNe) ring laser coupled to a passive enhancement resonator, which has been named a fast-light-enhanced HeNe ring-laser gyroscope (RLG). Theoretical rotation sensitivity enhancements as large as two orders of magnitude are presented. The physical effect responsible for the increased rotational sensitivity is the anomalous dispersion of the enhancement resonator, which produces a larger beat frequency as compared to a standard HeNe ring-laser gyroscope (RLG) as the laser cavity is rotated. We present the layout of the fast-light enhanced HeNe RLG, and we provide the theoretical modeling of the enhanced rotational sensitivity. A design is presented for the red HeNe (632.8 nm). The beat frequency is calculated with respect to rotation rate, which defines the useful range of operation for this highly sensitive RLG. Considerations for practical issues including laser-mirror reflectivity precision, unsaturated laser gain, and cavity-length stability are discussed.

Previously, we proposed a data buffering system that makes use of a pair of white light cavities 1 . For application to telecommunication systems, it would be convenient to realize such a device using fiber optic resonators. In this paper, we present the design of such a system, where the white light cavity effect is produced by using stimulated Brillouin scattering. The system consists of a pair of fiber optic white light cavities placed in series. As in the original proposal, the delay time can be controlled independently of the bandwidth of the data pulses. Furthermore, we show how the bandwidth of the system can be made as large as several times the Brillouin frequency shift. We also show that the net delay achievable in such a buffer can be significantly larger than what can be achieved using a conventional recirculating loop buffer.

We present a protocol for an atomic interferometer that reaches the Heisenberg Limit (HL), within a factor of ∼ √ 2, via collective state detection and critical tuning of one-axis twist spin squeezing. It generates a Schrödinger cat (SC) state, as a superposition of two extremal collective states. When this SC interferometer is used as a gyroscope, the interference occurs at an ultrahigh Compton frequency, corresponding to a mesoscopic single object with a mass of N m, where N is the number of particles in the ensemble, and m is the mass of each particle. For 87 Rb atoms, with N = 10 6 , for example, the intereference would occur at a Compton frequency of ∼ 2 × 10 31 Hz. Under this scheme, the signal is found to depend critically on the parity of N . We present two variants of the protocol. Under Protocol A, the fringes are narrowed by a factor of N for one parity, while for the other parity the signal is zero. Under Protocol B, the fringes are narrowed by a factor of N for one parity, and by a factor of √ N for the other parity. Both protocols can be modified in a manner that reverses the behavior of the signals for the two parities. Over repeated measurements under which the probability of being even or odd is equal, the averaged sensitivity is smaller than the HL by a factor of ∼ √ 2 for both versions of the protocol. We describe an experimental scheme for realizing such an atomic interferometer, and discuss potential limitations due to experimental constraints imposed by the current state of the art, for both collective state detection and oneaxis-twist squeezing. We show that when the SC interferometer is configured as an accelerometer, the effective two-photon wave vector is enhanced by a factor of N , leading to the same degree of enhancement in sensitivity. We also show that such a mesoscopic single object can be used to increase the effective base frequency of an atomic clock by a factor of N , with a sensitivity that is equivalent to the HL, within a factor of ∼ √ 2.

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We have demonstrated a laser in which the frequency shift due to small cavity fluctuations is far less than what would be expected from a conventional laser. The factor of sensitivity suppression is inferred to be equal to the effective group index experienced by the laser, implying that this laser is subluminal. We have observed a suppression factor as high as 663. Such a laser is highly self-stabilized compared to a conventional laser, and is expected to have a far smaller Schawlow-Townes linewidth. As a result, this laser may have potentially significant applications in the fields of high-precision optical metrology and passive frequency stabilization.