Communication through quantum-controlled noise

Guérin, Philippe; Rubino, Giulia; Brukner, Časlav

doi:10.1103/physreva.99.062317

Cited by 76 publications

(72 citation statements)

References 39 publications

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“…Abbott et al submit that the one-pass quantum superposition of two channels, without the indefinite causal order, already leads to a similar result [8]. This position has recently been supported in a different mathematical setting by Allard et al [9]. After introducing basic mathematical concepts in Section II, we explore the controversial origin of this advantage in Section III by simulating large sets of random channels.…”

Section: Introductionmentioning

confidence: 59%

“…When its action lowers the communication capacity of C, the likely origin of this effect has to do with the loss of information in diagonal terms C • C. When, on the contrary, the quantum switch yields an advantage over the superposition, the origin of this advantage belongs with non-diagonal terms. Heuristically, the non-diagonal terms in (9) are more versatile than the non-diagonal terms in (7), explaining the behaviour of the switch in Figure 5. The following argument provides evidence for the observation, made by Ebler et al, that an advantage occurs when the Kraus operators do not commute [7].…”

Section: Discussionmentioning

confidence: 99%

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Channel capacity enhancement with indefinite causal order

Loizeau

Grinbaum

2020

Phys. Rev. A

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Classical communication capacity of a channel can be enhanced either through a device called a 'quantum switch' or by putting the channel in a quantum superposition. The gains in the two cases, although different, have their origin in the use of a quantum resource, but is it the same resource? Here this question is explored through simulating large sets of random channels. We find that quantum superposition always provides an advantage, while the quantum switch does not: it can either increase or decrease communication capacity. The origin of this discrepancy can be attributed to a subtle combination of superposition and non-commutativity.

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Section: Introductionmentioning

confidence: 59%

Section: Discussionmentioning

confidence: 99%

Channel capacity enhancement with indefinite causal order

Loizeau

Grinbaum

2020

Phys. Rev. A

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“…Similar questions, as well as the need to clarify how to compare different such advantages, have also been raised recently based on different considerations in Ref. [40], and subsequently discussed further in Ref. [41].…”

Section: Communication Through Coherentlycontrolled Depolarising Chanmentioning

confidence: 78%

“…This is conceptually similar to the effect of quantum phase kickback associated with controlled unitary operations [1,45], and its role in such communication advantages is further explored in Refs. [40,41,44].…”

Section: Communication Through Coherentlycontrolled Depolarising Chanmentioning

confidence: 99%

Communication through coherent control of quantum channels

Abbott

Wechs

Horsman

et al. 2020

Quantum

118

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A completely depolarising quantum channel always outputs a fully mixed state and thus cannot transmit any information. In a recent Letter\cite{ebler18}, it was however shown that if a quantum state passes through two such channels in a quantum superposition of different orders---a setup known as the ``quantum switch''---then information can nevertheless be transmitted through the channels. Here, we show that a similar effect can be obtained when one coherently controls between sending a target system through one of two identical depolarising channels. Whereas it is tempting to attribute this effect in the quantum switch to the indefinite causal order between the channels, causal indefiniteness plays no role in this new scenario. This raises questions about its role in the corresponding effect in the quantum switch. We study this new scenario in detail and we see that, when quantum channels are controlled coherently, information about their specific implementation is accessible in the output state of the joint control-target system. This allows two different implementations of what is usually considered to be the same channel to therefore be differentiated. More generally, we find that to completely describe the action of a coherently controlled quantum channel, one needs to specify not only a description of the channel (e.g., in terms of Kraus operators), but an additional ``transformation matrix'' depending on its implementation.

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“…We note that when [6] proposed communication advantage from indefinite causal order they did not claim that the advantage is unique to coherent superposition of order. Subsequently, there has been an active discussion on the origin of the communication advantage [15][16][17] with consensus yet to be reached. The experimental developments in the present work and [13] are further motivation to develop a well-defined resource communication theory featuring coherence.…”

Section: A Two Depolarizing Channelsmentioning

confidence: 99%

Increasing communication capacity via superposition of order

Goswami

Cao

Paz-Silva

et al. 2020

Phys. Rev. Research

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Classically, no information can be transmitted through a depolarising, which is a completely noisy, channel. We show that by combining a depolarising channel with another channel in an indefinite causal order-that is, when there is a superposition of the order that these two channels were applied-it becomes possible to transmit significant information. We consider two limiting cases. When both channels are fully depolarising, the ideal limit is communication of 0.049 bits; experimentally we achieve (3.4 ± 0.2) × 10 −2 bits. When one channel is fully depolarising, and the other is a known unitary, the ideal limit is communication of 1 bit. We experimentally achieve 0.64 ± 0.02 bits. Our results offer intriguing possibilities for future communication strategies beyond conventional quantum Shannon theory.

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Communication through quantum-controlled noise

Cited by 76 publications

References 39 publications

Channel capacity enhancement with indefinite causal order

Channel capacity enhancement with indefinite causal order

Communication through coherent control of quantum channels

Increasing communication capacity via superposition of order

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