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arXiv:1403.6054 · Physical Review A

Heralded noiseless amplification and attenuation of non-Gaussian states of light

Christos N. Gagatsos, Jaromı́r Fiurášek, Alessandro Zavatta, Marco Bellini, Nicolas J. Cerf

Published Jun 9, 2014• 42 citations
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Abstract

We examine the behavior of non-Gaussian states of light under the action of probabilistic noiseless amplification and attenuation. Surprisingly, we find that the mean-field amplitude may decrease in the process of noiseless amplification---or may increase in the process of noiseless attenuation, a counterintuitive effect that Gaussian states cannot exhibit. This striking phenomenon could be tested with experimentally accessible non-Gaussian states, such as single-photon added coherent states. We propose an experimental scheme, which is robust with respect to the major experimental imperfections, such as inefficient single-photon detection and imperfect photon addition. In particular, we argue that the observation of mean-field amplification by noiseless attenuation should be feasible with current technology.

DOI
10.1103/physreva.89.062311

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We examine the behavior of non-Gaussian states of light under the action of probabilistic noiseless amplification and attenuation. Surprisingly, we find that the mean-field amplitude may decrease in the process of noiseless amplification---or may increase in the process of noiseless attenuation, a counterintuitive effect that Gaussian states cannot exhibit. This striking phenomenon could be tested with experimentally accessible non-Gaussian states, such as single-photon added coherent states. We propose an experimental scheme, which is robust with respect to the major experimental imperfections, such as inefficient single-photon detection and imperfect photon addition. In particular, we argue that the observation of mean-field amplification by noiseless attenuation should be feasible with current technology.
Loss suppression is a major challenge in quantum communication and quantum computing, primarily due to the limitations imposed by the no-cloning theorem. We present a noiseless quantum amplifier capable of probabilistically increasing the amplitude of coherent states without introducing additional noise to the amplified state. This is achieved through the conditional addition and subtraction of photons. Previously, experimental photon addition was restricted to a single photon. Recently, we have pushed these boundaries, demonstrating photon addition of up to three photons for the first time [1], as well as the combination of conditional addition of two photons followed by their conditional subtraction [2]. Our advanced noiseless amplifier achieves high amplification gain, fidelity, and purity, with the quadrature variances of the noiselessly amplified coherent states remaining close to the minimum uncertainty limit. Figure 1 illustrates the performance of our amplifier compared to that of an amplifier based on single-photon addition and subtraction.
Noiseless quantum amplifiers are probabilistic quantum devices that enhance the amplitude of coherent states without adding any noise, which has far reaching applications in quantum optics and quantum information processing. Here, we report on an experimental implementation of an advanced noiseless quantum amplifier for coherent states of light that is based on the conditional addition of two photons followed by the conditional subtraction of two photons. We comprehensively characterize the noiselessly amplified coherent states via quantum state tomography and analyze the amplification gain and noise properties of the amplifier. We observe very good agreement between the experiment and theoretical predictions. Our work reveals that sequences of multiple photon additions and subtractions represent an efficient and experimentally feasible alternative to multiplexing that was originally proposed to boost the performance of noiseless quantum amplifiers. Beyond noiseless quantum amplification, our experiment represents a significant step forward towards engineering complex quantum operations on traveling light beams by coherent combinations of various sequences of multiphoton additions and subtractions.
Noiseless quantum amplifiers are probabilistic quantum devices that enhance amplitude of coherent states without adding any noise, which has far reaching applications in quantum optics and quantum information processing. Here, we report on experimental implementation of an advanced noiseless quantum amplifier for coherent states of light that is based on conditional addition of two photons followed by conditional subtraction of two photons. We comprehensively characterize the noiselessly amplified coherent states via quantum state tomography and analyze the amplification gain and noise properties of the amplifier. We observe very good agreement between the experiment and theoretical predictions. Our work reveals that sequences of multiple photon additions and subtractions represent an efficient and experimentally feasible alternative to multiplexing that was originally proposed to boost the performance of noiseless quantum amplifiers. Beyond noiseless quantum amplification, our experiment represents a significant step forward towards engineering complex quantum operations on traveling light beams by coherent combinations of various sequences of multiphoton additions and subtractions.
Quantum-limited amplifiers increase the amplitude of quantum signals at the price of introducing additional noise. Quantum purification protocols operate in the reverse way, by reducing the noise while attenuating the signal. Here we investigate a scenario that interpolates between these two extremes. We search for the optimal physical process that generates MMM approximate copies of a pure and amplified coherent state, starting from NNN copies of a noisy coherent state with Gaussian modulation. We prove that the optimal deterministic processes are always Gaussian, whereas non-Gaussianity powers up probabilistic advantages in suitable parameter regimes. The optimal processes are experimentally realizable with current technology, both in the deterministic and in the probabilistic scenario. In view of this fact, we provide benchmarks that can be used to certify the experimental demonstration of the quantum-enhanced amplification and purification of coherent states.
We suggest and investigate a scheme for non-deterministic noiseless linear amplification of coherent states using successive photon addition, (â(†))(2), where â(†) is the photon creation operator. We compare it with a previous proposal using the photon addition-then-subtraction, ââ(†), where â is the photon annihilation operator, that works as an appropriate amplifier only for weak light fields. We show that when the amplitude of a coherent state is |α| ≳ 0.91, the (â(†))(2) operation serves as a more efficient amplifier compared to the ââ(†) operation in terms of equivalent input noise. Using ââ(†) and (â(†))(2) as basic building blocks, we compare combinatorial amplifications of coherent states using (ââ(†))(2), â(†4), ââ(†)â(†2), and â(†2)ââ(†), and show that (ââ(†))(2), â(†2)ââ(†), and â(†4) exhibit strongest noiseless properties for |α| ≲ 0.51, 0.51 ≲ |α| ≲ 1.05, and |α| ≳ 1.05, respectively. We further show that the (â(†))(2) operation can be useful for amplifying superpositions of the coherent states. In contrast to previous studies, our work provides efficient schemes to implement a noiseless amplifier for light fields with medium and large amplitudes.
We show that the use of probabilistic noiseless amplification in entangled coherent state-based schemes for the test of quantum non locality provides significant advantages. The threshold amplitude to falsify a Bell-CHSH non locality test, in fact, is significantly reduced when amplification is embedded into the test itself, while any detection-inefficiency effect can be effectively compensated by tuning the amplification gain. We extend our analysis to general tests of quantum non locality in phase space, therefore affirming noiseless amplification as a valuable tool for coherent information processing and the generation of strongly non-classical states of bosonic systems.