Communication through coherent control of quantum channels
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...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
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Verein zur Förderung des Open Access Publizierens in den Quantenwissenschaften
2020-09-01
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| Series: | Quantum |
| Online Access: | https://quantum-journal.org/papers/q-2020-09-24-333/pdf/ |
| _version_ | 1828155717013471232 |
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| author | Alastair A. Abbott Julian Wechs Dominic Horsman Mehdi Mhalla Cyril Branciard |
| author_facet | Alastair A. Abbott Julian Wechs Dominic Horsman Mehdi Mhalla Cyril Branciard |
| author_sort | Alastair A. Abbott |
| collection | DOAJ |
| description | 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. |
| first_indexed | 2024-04-11T22:58:11Z |
| format | Article |
| id | doaj.art-0fcf8e7355074eb5b88a1dc2e1bf1220 |
| institution | Directory Open Access Journal |
| issn | 2521-327X |
| language | English |
| last_indexed | 2024-04-11T22:58:11Z |
| publishDate | 2020-09-01 |
| publisher | Verein zur Förderung des Open Access Publizierens in den Quantenwissenschaften |
| record_format | Article |
| series | Quantum |
| spelling | doaj.art-0fcf8e7355074eb5b88a1dc2e1bf12202022-12-22T03:58:17ZengVerein zur Förderung des Open Access Publizierens in den QuantenwissenschaftenQuantum2521-327X2020-09-01433310.22331/q-2020-09-24-33310.22331/q-2020-09-24-333Communication through coherent control of quantum channelsAlastair A. AbbottJulian WechsDominic HorsmanMehdi MhallaCyril BranciardA 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.https://quantum-journal.org/papers/q-2020-09-24-333/pdf/ |
| spellingShingle | Alastair A. Abbott Julian Wechs Dominic Horsman Mehdi Mhalla Cyril Branciard Communication through coherent control of quantum channels Quantum |
| title | Communication through coherent control of quantum channels |
| title_full | Communication through coherent control of quantum channels |
| title_fullStr | Communication through coherent control of quantum channels |
| title_full_unstemmed | Communication through coherent control of quantum channels |
| title_short | Communication through coherent control of quantum channels |
| title_sort | communication through coherent control of quantum channels |
| url | https://quantum-journal.org/papers/q-2020-09-24-333/pdf/ |
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