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Room temperature conditional $\pi$-phase shifts mediated by simultaneously propagating single-photon level pulses

Reihaneh Shahrokhshahi, Steven Sagona-Stophel, Bertus Jordaan, Mehdi Namazi, Eden V. Figueroa

Published Mar 19, 2018• 0 citations
OpenAlex

Abstract

Here we demonstrate the first room-temperature implementation of $\pi$ phase shifts in single-photon-level probe light created by a simultaneously propagating few-photon triggering signal field. The photon-photon interaction is mediated by rubidium atoms in a double $\Lambda$ atomic scheme. We use homodyne tomography and maximum likelihood estimation on the quadrature statistics of the input and phase-shifted photons to fully characterize their quantum states in the Fock state basis. For particular choices in control fields strengths and input phases, the input-output fidelity of the controlled $\pi$ phase shift operation reaches $\sim$90$\%$.

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Room temperature conditional π\piπ-phase shifts mediated by simultaneously propagating single-photon level pulses
Here we demonstrate the first room-temperature implementation of π\piπ phase shifts in single-photon-level probe light created by a simultaneously propagating few-photon triggering signal field. The photon-photon interaction is mediated by rubidium atoms in a double Λ\LambdaΛ atomic scheme. We use homodyne tomography and maximum likelihood estimation on the quadrature statistics of the input and phase-shifted photons to fully characterize their quantum states in the Fock state basis. For particular choices in control fields strengths and input phases, the input-output fidelity of the controlled π\piπ phase shift operation reaches ∼\sim∼90%\%%.
The development of useful photon-photon interactions can trigger numerous breakthroughs in quantum information science, however, this has remained a considerable challenge spanning several decades. Here, we demonstrate the first room-temperature implementation of large phase shifts (≈π) on a single-photon level probe pulse (1.5 μs) triggered by a simultaneously propagating few-photon-level signal field. This process is mediated by Rb^{87} vapor in a double-Λ atomic configuration. We use homodyne tomography to obtain the quadrature statistics of the phase-shifted quantum fields and perform maximum-likelihood estimation to reconstruct their quantum state in the Fock state basis. For the probe field, we have observed input-output fidelities higher than 90% for phase-shifted output states, and high overlap (over 90%) with a theoretically perfect coherent state. Our noise-free, four-wave-mixing-mediated photon-photon interface is a key milestone toward developing quantum logic and nondemolition photon detection using schemes such as coherent photon conversion.
Any optical quantum information processing machine would be comprised of fully-characterized constituent devices for both single state manipulations and tasks involving the interaction between multiple quantum optical states. Ideally for the latter, would be an apparatus capable of deterministic optical phase shifts that operate on input quantum states with the action mediated solely by auxiliary signal fields. Here we present the complete experimental characterization of a system designed for optically controlled phase shifts acting on single-photon level probe coherent states. Our setup is based on a warm vapor of rubidium atoms under the conditions of electromagnetically induced transparency with its dispersion properties modified through the use of an optically triggered N-type Kerr non-linearity. We fully characterize the performance of our device by sending in a set of input probe states and measuring the corresponding output via balanced homodyne tomography and subsequently performing the technique of coherent state quantum process tomography. This method provides us with the precise knowledge of how our optical phase shift will modify any arbitrary input quantum state engineered in the mode of the reconstruction.
Any optical quantum information processing machine would be comprised of fully-characterized constituent devices for both single state manipulations and tasks involving the interaction between multiple quantum optical states. Ideally for the latter, would be an apparatus capable of deterministic optical phase shifts that operate on input quantum states with the action mediated solely by auxiliary signal fields. Here we present the complete experimental characterization of a system designed for optically controlled phase shifts acting on single-photon level probe coherent states. Our setup is based on a warm vapor of rubidium atoms under the conditions of electromagnetically induced transparency with its dispersion properties modified through the use of an optically triggered N-type Kerr non-linearity. We fully characterize the performance of our device by sending in a set of input probe states and measuring the corresponding output via time-domain homodyne tomography and subsequently performing the technique of coherent state quantum process tomography. This method provides us with the precise knowledge of how our optical phase shift will modify any arbitrary input quantum state engineered in the mode of the reconstruction.
Using a polarization-selective-Kerr-phase-shift technique we demonstrate a fast, all-optical, high-fidelity polarization gate in a room-temperature atomic medium. By writing a π- phase shift to one selected circularly-polarized component of a linearly-polarized input signal field and by equalizing the gain of both circularly-polarized components we can maintain the original strength of the signal field and yet achieve a perfect 90° rotation of its linear polarization, demonstrating a fast, high-fidelity, dynamically-controlled polarization gate operation. The orthogonal linear polarization switching field intensity can be as low as 2 mW/cm 2 using a warm rubidium vapor, which is equivalent to a 100-nanosecond pulse containing about 200 photons and confined in a typical commercial photonic hollow-core fiber with a 5-μm mode diameter.
Summary form only given. Achieving photon-photon interactions is one of the main objectives of the quantum information technology community, since these interactions provide the basis for deterministic quantum gates with high fidelity. In the last few years new milestones in creating phase-shifts [1] and quantum gates[2] have been achieved. Researching resource-moderate experimental realizations for the future development of this field provides a scalable framework for devices and opportunities for deployment in quantum communication networks.We highlight photon-photon interactions in unexplored physical regimes that are outside the standard approach of single atom QED or Rydberg transitions. Building on the first complete quantum optical characterization of an engineered free space phase shift triggered via atomic Kerr nonlinearities [3], we characterize novel architectures using the interaction of single photons in both a room temperature atomic vapor and cold atomic ensembles in miniaturized cavity QED setups. These different systems provide very compelling pathways to achieving photonphoton interactions.
We demonstrate a fast, all-optical polarization gate in a room-temperature atomic medium. Using a Polarization-Selective-Kerr-Phase-Shift (PSKPS) technique, we selectively write a π phase shift to one circularly-polarized component of a linearly-polarized input signal field. The output signal field maintains its original strength but acquires a 90° linear polarization rotation, demonstrating fast, high-fidelity, dynamically-controlled polarization gate operation. The intensity of the polarization-switching field used in this PKSPK-based polarization gate operation is only 2 mW/cm2, which would be equivalent to 0.5 nW of light power (λ = 800 nm) confined in a typical commercial photonic hollow-core fiber. This development opens a realm of possibilities for potential future extremely low light level telecommunication and information processing systems.