• Corpus ID: 252368210

Witnessing superpositions of causal orders by weak measurements at a given time

  title={Witnessing superpositions of causal orders by weak measurements at a given time},
  author={Onur Pusuluk and Z Gedik and Vlatko Vedral},
The questions we raise in this letter are as follows: What is the most general representation of a quantum state at a single time? Can we adapt the current representations to the scenarios in which the order of quantum operations are coherently or incoherently superposed? If so, what is the relation between the state at a given time and the uncertainty in the order of events before and after it? By establishing the relationship of two-state vector formalism with pseudo-density operators, we… 

Figures from this paper



Quantum correlations which imply causation

This work introduces the concept of a pseudo-density matrix (PDM) which treats space and time indiscriminately and defines a measure of causality that discriminates between spatial and temporal correlations.

Quantum correlations with no causal order

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.

Experimental verification of an indefinite causal order

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.

Witnessing causal nonseparability

This work shows that a recently demonstrated resource for quantum computation—the quantum switch—is a genuine example of 'indefinite causal order', and introduces a new tool—the causal witness—which can detect the causal nonseparability of any quantum resource that is incompatible with a definite causal order.

The Two-State Vector Formalism: An Updated Review

The two-state vector formalism of quantum mechanics is a time-symmetrized approach to standard quantum theory particularly helpful for the analysis of experiments performed on preand post-selected

Experimental superposition of orders of quantum gates

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.

Complete description of a quantum system at a given time

A generalization of the description of a quantum system in the time interval between two measurements is presented. A new concept of a generalized state is introduced. Generalized states yield a

Enhanced Communication with the Assistance of Indefinite Causal Order.

This Letter shows that two identical copies of a completely depolarizing channel become able to transmit information when they are combined in a quantum superposition of two alternative orders, counter to the intuition that if two communication channels are identical, using them in different orders should not make any difference.

Quantum correlations in the temporal Clauser–Horne–Shimony–Holt (CHSH) scenario

We consider a temporal version of the Clauser–Horne–Shimony–Holt (CHSH) scenario using projective measurements on a single quantum system. It is known that quantum correlations in this scenario are

Quantum computations without definite causal structure

It is shown that quantum theory allows for transformations of black boxes that cannot be realized by inserting the input black boxes within a circuit in a pre-defined causal order, and that the quantum version of this transformation-the quantum switch- produces an output circuit where the order of the connections is controlled by a quantum bit, which becomes entangled with the circuit structure.