Increasing communication capacity via superposition of order

Goswami, Kaumudibikash; Cao, Ye; Paz-Silva, Gerardo A.; Romero, Jacquiline; White, A. G.

doi:10.1103/physrevresearch.2.033292

Cited by 73 publications

(58 citation statements)

References 16 publications

(31 reference statements)

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“…Thus far, all attempts to implement the quantum switch have relied on interferometric setups [16][17][18][19][20][21][22]31]. 1 In a typical such setup, the target system is routed to the switched operations, which here correspond to communication channels, via some beamsplitters (see insert of Fig.…”

Section: Communication Through Coherentlycontrolled Depolarising Chanmentioning

confidence: 99%

“…[3] and implemented experimentally in Refs. [20,22] (for the case of a qubit target system, d = 2) where these are realised by randomising over a set of…”

Section: Communication Through Coherentlycontrolled Depolarising Chanmentioning

confidence: 99%

“…The quantum switch is, more formally, a "quantum supermap" [11], and its causal indefiniteness can be formally understood through the notion of "causal nonseparability" [12][13][14][15]. Several recent experiments have been conducted to implement the quantum switch and experimentally verify its causal indefiniteness [16][17][18][19][20][21][22].…”

Section: Introductionmentioning

confidence: 99%

“…individually. This somewhat surprising result arising in the presence of indefinite causal order has recently been subject to experimental tests [20,22], and generalised to setups that put more channels in a superposition of different orders [29,30]. Note that S[N 0 , N 1 ] above-and more generally, S[C 0 , C 1 ]-depend only on the CPTP maps implemented by the black-box operations, despite the fact the operations are applied only to a subspace of the joint target-control space [2,3]; this is a consequence of the quantum switch being a quantum supermap.…”

Section: Introductionmentioning

confidence: 99%

“…in Refs. [19,20]). In the present work we consider only the "first half" of such a setup, as shown in the main figure.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Communication Through Coherentlycontrolled Depolarising Chanmentioning

confidence: 99%

“…[3] and implemented experimentally in Refs. [20,22] (for the case of a qubit target system, d = 2) where these are realised by randomising over a set of…”

Section: Communication Through Coherentlycontrolled Depolarising Chanmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…in Refs. [19,20]). In the present work we consider only the "first half" of such a setup, as shown in the main figure.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Communication through coherent control of quantum channels

Abbott

Wechs

Horsman

et al. 2020

Quantum

118

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Experimentally Demonstrating Indefinite Causal Order Algorithms to Solve the Generalized Deutsch's Problem

Liu,

Meng,

Song

et al. 2024

Adv Quantum Tech

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Deutsch's algorithm is the first quantum algorithm to demonstrate an advantage over classical algorithms. Here, Deutsch's problem is generalized to functions and a quantum algorithm with an indefinite causal order is proposed to solve this problem. The algorithm not only reduces the number of queries to the black box by half compared to the classical algorithm, but also significantly decreases the complexity of the quantum circuit and the number of required quantum gates compared to the generalized Deutsch's algorithm. The algorithm is experimentally demonstrated in a stable Sagnac loop interferometer with a common path, which overcomes the obstacles of both phase instability and low fidelity of the Mach–Zehnder interferometer. The experimental results show both ultrahigh and robust success probabilities . This study opens a path toward solving practical problems with indefinite cause‐order quantum circuits.

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