Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Physical Review A

Benchmarking the state comparison amplifier

Klaudia Kleczkowska, Ittoop Vergheese Puthoor, Lauren Bain, Erika Andersson

Published Oct 9, 2017• 1 citation
Publisher

Abstract

The state comparison amplifier is a recently proposed probabilistic quantum amplifier, intended especially for amplifying coherent states. Its realization is simple and uses only linear optics and photodetectors, and the preparation of a ``guess'' state, typically a coherent state. Fidelity and success probability can be high compared with other probabilistic amplifiers. State comparison amplification does, however, extract information about the amplified state, which means that it is especially important to benchmark it against a simple measure-and-resend procedure. We compare state comparison quantum amplifiers to measure-and-resend strategies, and identify parameter regimes and scenarios where these can and where they cannot provide an advantage.

DOI
10.1103/physreva.96.042309

Related papers

Quantum state comparison amplifier with feedforward state correction

Luca Mazzarella, Ross J. Donaldson, Robert John Collins +4 more

Quantum mechanics imposes stringent constraints on the amplification of a quantum signal. Deterministic amplification of an unknown quantum state always implies the addition of a minimal amount of noise. Linear and noiseless amplification is allowed in principle provided that it only works probabilistically. Here we present a probabilistic amplifier that combines two quantum state comparison amplifiers (SCAMP) together with a feed-forward state correction strategy. Our system outperforms the unambiguous state discrimination (USD) measure-and-resend based amplifier in terms of the success probability-fidelity product and requires a more complex experimental setting.

SPIE Quantum Technologies•May 21, 2018•3 citations

A learning scheme with coherent state receiver (Conference Presentation)

Luca Mazzarella, Ross J. Donaldson, Robert John Collins +5 more

The laws of quantum mechanics pose stringent constraints on the amplification of a quantum signal. Deterministic amplification of an unknown quantum state always implies the addition of a minimal amount of noise. In principle, linear and noiseless amplification is allowed provided it works only probabilistically [1,2]. The state comparison amplifier [3] is an approximate probabilistic amplifier that amplifies a coherent state chosen at random from a set of coherent states with known mean photon number. The amplification process works as follows: Alice picks uniformly at random an input state and passes it to Bob. He desires to amplify the state so he mixes it with a guess coherent state at a beam splitter in an attempt to achieve destructive interference in one of the output arms. This output is fed into an APD detector. The lack of trigger at the detector is an imperfect indication that Bob’s guess is right and that the output contains the correct amplified state. On the other hand, if the first detector fires Bob knows that his guess was wrong but he can still correct the output by changing the input state for a second amplification stage via a feed-forward loop. In summary, Bob declares success when both the detectors do not fire or when the first detector does fire and state correction is performed. We generalize this mechanism for an arbitrary number of input states and beam splitters, using an on-line learning strategy based on maximum a posteriori probability. The success probability-fidelity product [2] of the SCAMP is the joint probability of success and of passing a measurement test on the output comparing it to right amplified state. Our figures of merit compare favorably with other schemes. The success probability-fidelity product of the SCAMP is always bigger than that of a USD based amplifier [2] that, when inconclusive, delivers a conveniently chosen random output. The SCAMP can be realized with classical resources (i.e., lasers, linear optics and APD detectors), the ability to switch between input states on the fly requires delay lines and fast switching but it can still be achieved with classical resources and the loss introduced by the delay can be offset at the second stage. Similar systems, with no state correction, proved to achieve high-gain, high fidelity and high repetition rates, e.g. [4, 5]. Due to its simplicity, the system we propose might represent an ideal candidate either as a recovery station to counteract quantum signal degradation due to propagation in a lossy fibre or across the turbulent atmosphere or as a quantum receiver to improve the key-rate of continuous-variable quantum key distribution with discrete modulation. The system is also suitable for on-chip implementation. [1] T.C. Ralph & A.P. Lund, Proceedings of the 9th QCMC Conference 2009. [2] S. Pandey, et al., Phys. Rev. A 88, 033852 (2013). [3] E. Eleftheriadou et al., Phys. Rev. Lett. 111, 213601 (2013). [4] R. Donaldson et al., Phys. Rev. Lett. 114, 120505 (2015). [5] R. Donaldson et al., in preparation.

SPIE Quantum Information Science and Technology•Oct 11, 2018•0 citations

A high-gain and high-fidelity coherent state comparison amplifier

Ross J. Donaldson, Luca Mazzarella, Robert John Collins +2 more

Abstract Optical signals are subject to a distance-dependent loss as they propagate through transmission media. High-intensity, classical, optical signals can routinely be amplified to overcome the degradation caused by this loss. However, quantum optical states cannot be deterministically amplified and any attempt to do so will introduce intrinsic noise that spoils the desired quantum properties. Non-deterministic optical amplification, based on post-selection of the output depending on certain conditioning detection outcomes, is an emerging enabling technology in quantum measurement and quantum communications. Here we present an investigation into the properties of a simple, modular optical state comparison amplifier operating on weak coherent states. This amplifier requires no complex quantum resources and is based on linear optical components allowing for a high amplification rate at high gain and fidelity. We examine the amplifier’s performance in different configurations and develop an accurate analytical model that accounts for typical experimental scenarios.

Communications Physics•Sep 6, 2018•16 citations

Feedforward-assisted coherent-state comparison amplifier

M. Bathaee, N. Marjan, Alireza Bahrampour

Quantum optical coherent-state comparison amplifiers are nondeterministic devices which can amplify rather noiselessly a weak coherent state with an unknown phase from a finite discrete set. The high fidelity and high success probability of this amplifier are accomplished by a comparison stage and some photon subtraction stages. Due to the heralding nature of these amplifiers, they work part of the time. Here, we propose a feedforward protocol to increase the heralded times by correcting the incorrect guess. Hence, we enhance the fidelity and success probability more. Finally, the schematic experimental configuration of the feedforward-assisted coherent-state comparison amplifier is proposed.

Physical Review A•Oct 8, 2019•1 citation

Quantum Optical State Comparison Amplifier

Electra Eleftheriadou, Stephen Mark Barnett, John Jeffers

It is a fundamental principle of quantum theory that an unknown state cannot be copied or, as a consequence, an unknown optical signal cannot be amplified deterministically and perfectly. Here we describe a protocol that provides nondeterministic quantum optical amplification in the coherent state basis with high gain and high fidelity and which does not use quantum resources. The scheme is based on two mature quantum optical technologies: coherent state comparison and photon subtraction. The method compares favorably with all previous nondeterministic amplifiers in terms of fidelity and success probability.

arXiv:1311.5730•Physical Review Letters•Nov 19, 2013•28 citations

Quantum state correction using a measurement-based feedforward mechanism

Ross J. Donaldson, Luca Mazzarella, Ugo Zanforlin +3 more

One of the weaknesses of quantum optical state postselection schemes is the low success probability. Typically there is a trade-off between amplifier properties such as success probability and output state fidelity. However, here we present a state comparison amplifier for optical coherent states, which features an active measurement and feedforward mechanism to correct for errors made during the initial amplification. The simple and relatively low latency mechanism allows us to correct for a binary phase alphabet. We demonstrate a significant simultaneous improvement in the amplifier characteristic parameters: output state fidelity, correct state fraction, and success probability. This demonstrates that nondeterministic quantum amplification can be enhanced significantly by measurement and feedforward.

Physical Review A•Aug 26, 2019•11 citations
The state comparison amplifier is a recently proposed probabilistic quantum amplifier, intended especially for amplifying coherent states. Its realization is simple and uses only linear optics and photodetectors, and the preparation of a ``guess'' state, typically a coherent state. Fidelity and success probability can be high compared with other probabilistic amplifiers. State comparison amplification does, however, extract information about the amplified state, which means that it is especially important to benchmark it against a simple measure-and-resend procedure. We compare state comparison quantum amplifiers to measure-and-resend strategies, and identify parameter regimes and scenarios where these can and where they cannot provide an advantage.
Quantum mechanics imposes stringent constraints on the amplification of a quantum signal. Deterministic amplification of an unknown quantum state always implies the addition of a minimal amount of noise. Linear and noiseless amplification is allowed in principle provided that it only works probabilistically. Here we present a probabilistic amplifier that combines two quantum state comparison amplifiers (SCAMP) together with a feed-forward state correction strategy. Our system outperforms the unambiguous state discrimination (USD) measure-and-resend based amplifier in terms of the success probability-fidelity product and requires a more complex experimental setting.
The laws of quantum mechanics pose stringent constraints on the amplification of a quantum signal. Deterministic amplification of an unknown quantum state always implies the addition of a minimal amount of noise. In principle, linear and noiseless amplification is allowed provided it works only probabilistically [1,2]. The state comparison amplifier [3] is an approximate probabilistic amplifier that amplifies a coherent state chosen at random from a set of coherent states with known mean photon number. The amplification process works as follows: Alice picks uniformly at random an input state and passes it to Bob. He desires to amplify the state so he mixes it with a guess coherent state at a beam splitter in an attempt to achieve destructive interference in one of the output arms. This output is fed into an APD detector. The lack of trigger at the detector is an imperfect indication that Bob’s guess is right and that the output contains the correct amplified state. On the other hand, if the first detector fires Bob knows that his guess was wrong but he can still correct the output by changing the input state for a second amplification stage via a feed-forward loop. In summary, Bob declares success when both the detectors do not fire or when the first detector does fire and state correction is performed. We generalize this mechanism for an arbitrary number of input states and beam splitters, using an on-line learning strategy based on maximum a posteriori probability. The success probability-fidelity product [2] of the SCAMP is the joint probability of success and of passing a measurement test on the output comparing it to right amplified state. Our figures of merit compare favorably with other schemes. The success probability-fidelity product of the SCAMP is always bigger than that of a USD based amplifier [2] that, when inconclusive, delivers a conveniently chosen random output. The SCAMP can be realized with classical resources (i.e., lasers, linear optics and APD detectors), the ability to switch between input states on the fly requires delay lines and fast switching but it can still be achieved with classical resources and the loss introduced by the delay can be offset at the second stage. Similar systems, with no state correction, proved to achieve high-gain, high fidelity and high repetition rates, e.g. [4, 5]. Due to its simplicity, the system we propose might represent an ideal candidate either as a recovery station to counteract quantum signal degradation due to propagation in a lossy fibre or across the turbulent atmosphere or as a quantum receiver to improve the key-rate of continuous-variable quantum key distribution with discrete modulation. The system is also suitable for on-chip implementation. [1] T.C. Ralph & A.P. Lund, Proceedings of the 9th QCMC Conference 2009. [2] S. Pandey, et al., Phys. Rev. A 88, 033852 (2013). [3] E. Eleftheriadou et al., Phys. Rev. Lett. 111, 213601 (2013). [4] R. Donaldson et al., Phys. Rev. Lett. 114, 120505 (2015). [5] R. Donaldson et al., in preparation.
Abstract Optical signals are subject to a distance-dependent loss as they propagate through transmission media. High-intensity, classical, optical signals can routinely be amplified to overcome the degradation caused by this loss. However, quantum optical states cannot be deterministically amplified and any attempt to do so will introduce intrinsic noise that spoils the desired quantum properties. Non-deterministic optical amplification, based on post-selection of the output depending on certain conditioning detection outcomes, is an emerging enabling technology in quantum measurement and quantum communications. Here we present an investigation into the properties of a simple, modular optical state comparison amplifier operating on weak coherent states. This amplifier requires no complex quantum resources and is based on linear optical components allowing for a high amplification rate at high gain and fidelity. We examine the amplifier’s performance in different configurations and develop an accurate analytical model that accounts for typical experimental scenarios.
Quantum optical coherent-state comparison amplifiers are nondeterministic devices which can amplify rather noiselessly a weak coherent state with an unknown phase from a finite discrete set. The high fidelity and high success probability of this amplifier are accomplished by a comparison stage and some photon subtraction stages. Due to the heralding nature of these amplifiers, they work part of the time. Here, we propose a feedforward protocol to increase the heralded times by correcting the incorrect guess. Hence, we enhance the fidelity and success probability more. Finally, the schematic experimental configuration of the feedforward-assisted coherent-state comparison amplifier is proposed.
It is a fundamental principle of quantum theory that an unknown state cannot be copied or, as a consequence, an unknown optical signal cannot be amplified deterministically and perfectly. Here we describe a protocol that provides nondeterministic quantum optical amplification in the coherent state basis with high gain and high fidelity and which does not use quantum resources. The scheme is based on two mature quantum optical technologies: coherent state comparison and photon subtraction. The method compares favorably with all previous nondeterministic amplifiers in terms of fidelity and success probability.
One of the weaknesses of quantum optical state postselection schemes is the low success probability. Typically there is a trade-off between amplifier properties such as success probability and output state fidelity. However, here we present a state comparison amplifier for optical coherent states, which features an active measurement and feedforward mechanism to correct for errors made during the initial amplification. The simple and relatively low latency mechanism allows us to correct for a binary phase alphabet. We demonstrate a significant simultaneous improvement in the amplifier characteristic parameters: output state fidelity, correct state fraction, and success probability. This demonstrates that nondeterministic quantum amplification can be enhanced significantly by measurement and feedforward.