Quantum Metrology with Indefinite Causal Order.

@article{Zhao2020QuantumMW,
  title={Quantum Metrology with Indefinite Causal Order.},
  author={Xiaobin Zhao and Yuxiang Yang and Giulio Chiribella},
  journal={Physical review letters},
  year={2020},
  volume={124 19},
  pages={
          190503
        }
}
We address the study of quantum metrology enhanced by indefinite causal order, demonstrating a quadratic advantage in the estimation of the product of two average displacements in a continuous variable system. We prove that no setup where the displacements are used in a fixed order can have root-mean-square error vanishing faster than the Heisenberg limit 1/N, where N is the number of displacements contributing to the average. In stark contrast, we show that a setup that probes the… Expand

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References

SHOWING 1-10 OF 64 REFERENCES
Indefinite Causal Order in a Quantum Switch.
TLDR
A photonic quantum switch is realized, where two operations A and B act in a quantum superposition of their two possible orders, on the transverse spatial mode of the photons; polarization coherently controls their order. Expand
Experimental verification of an indefinite causal order
TLDR
Researchers report the first decisive demonstration of a process with an indefinite causal order, and experimentally determine a causal witness, demonstrating by almost 7 SDs that the experimentally implemented process does not have a definite causal order. Expand
Indefinite causal order aids quantum depolarizing channel identification
  • M. Frey
  • Computer Science, Mathematics
  • Quantum Inf. Process.
  • 2019
TLDR
This work uses quantum Fisher information to study a probing scheme in which the channel is put in indefinite causal order (ICO) with copies of itself, and shows that ICO-assisted probing yields greater information than does the comparable probe re-circulation scheme with definite causal order. Expand
Quantum metrology.
TLDR
It is proved that the typical quantum precision enhancement is of the order of the square root of the number of times the system is sampled, and it is pointed out the different strategies that permit one to attain this bound. Expand
Experimental superposition of orders of quantum gates
TLDR
This work experimentally demonstrates the creation of the required superposition of gate orders by using additional degrees of freedom of the photons encoding qubits, which could allow quantum algorithms to be implemented with an efficiency unlikely to be achieved on a fixed-gate-order quantum computer. Expand
Quantum correlations with no causal order
TLDR
It is shown that in a classical limit causal order always arises, which suggests that space-time may emerge from a more fundamental structure in a quantum-to-classical transition. Expand
Experimental Quantum Switching for Exponentially Superior Quantum Communication Complexity.
TLDR
The results elucidate the crucial role of the coherence of communication direction in achieving the exponential separation for the one-way processing task, and open a new path for experimentally exploring the fundamentals and applications of advanced features of indefinite causal structures. Expand
Computational advantage from quantum-controlled ordering of gates.
TLDR
It is shown that this model of quantum computing is physically realizable, by proposing an interferometric setup that can implement such a quantum control of the order between the gates, and that this new resource provides a reduction in computational complexity. Expand
Indefinite causal structures for continuous-variable systems
In all our well-established theories, it is assumed that events are embedded in a global causal structure such that, for every pair of events, the causal order between them is always fixed. However,Expand
Theoretical framework for higher-order quantum theory
TLDR
The present treatment provides a general framework where this kind of analysis can be carried out in full generality of higher-order quantum functions, and can be exported in the context of any operational probabilistic theory. Expand
...
1
2
3
4
5
...