scholarly journals Quantum Circuits with Classical Versus Quantum Control of Causal Order

PRX Quantum ◽  
2021 ◽  
Vol 2 (3) ◽  
Author(s):  
Julian Wechs ◽  
Hippolyte Dourdent ◽  
Alastair A. Abbott ◽  
Cyril Branciard
Keyword(s):  
Quantum Control ◽  
Quantum Circuits ◽  
Causal Order

scholarly journals Control aspects of quantum computing using pure and mixed states

2012 ◽  
Vol 370 (1976) ◽  
pp. 4651-4670 ◽  
Author(s):  
Thomas Schulte-Herbrüggen ◽  
Raimund Marx ◽  
Amr Fahmy ◽  
Louis Kauffman ◽  
Samuel Lomonaco ◽  
...  
Keyword(s):  
Quantum Dynamics ◽  
Quantum Control ◽  
Open Quantum Systems ◽  
Jones Polynomial ◽  
Ion Traps ◽  
Quantum States ◽  
Nitrogen Vacancy ◽  
Quantum Circuits ◽  
State Transfer ◽  
Hard Problems

Steering quantum dynamics such that the target states solve classically hard problems is paramount to quantum simulation and computation. And beyond, quantum control is also essential to pave the way to quantum technologies. Here, important control techniques are reviewed and presented in a unified frame covering quantum computational gate synthesis and spectroscopic state transfer alike. We emphasize that it does not matter whether the quantum states of interest are pure or not. While pure states underly the design of quantum circuits, ensemble mixtures of quantum states can be exploited in a more recent class of algorithms: it is illustrated by characterizing the Jones polynomial in order to distinguish between different (classes of) knots. Further applications include Josephson elements, cavity grids, ion traps and nitrogen vacancy centres in scenarios of closed as well as open quantum systems.

scholarly journals Consequences of preserving reversibility in quantum superchannels

Quantum ◽  
2021 ◽  
Vol 5 ◽  
pp. 441
Author(s):  
Wataru Yokojima ◽  
Marco Túlio Quintino ◽  
Akihito Soeda ◽  
Mio Murao
Keyword(s):  
Quantum Mechanics ◽  
Physical Interpretation ◽  
Quantum Circuit ◽  
Quantum States ◽  
Quantum Circuits ◽  
Causal Order ◽  
Quantum Operations ◽  
Coherent Superposition ◽  
Physical Implementation ◽  
Quantum Objects

Similarly to quantum states, quantum operations can also be transformed by means of quantum superchannels, also known as process matrices. Quantum superchannels with multiple slots are deterministic transformations which take independent quantum operations as inputs. While they are enforced to respect the laws of quantum mechanics, the use of input operations may lack a definite causal order, and characterizations of general superchannels in terms of quantum objects with a physical implementation have been missing. In this paper, we provide a mathematical characterization for pure superchannels with two slots (also known as bipartite pure processes), which are superchannels preserving the reversibility of quantum operations. We show that the reversibility preserving condition restricts all pure superchannels with two slots to be either a quantum circuit only consisting of unitary operations or a coherent superposition of two unitary quantum circuits where the two input operations are differently ordered. The latter may be seen as a generalization of the quantum switch, allowing a physical interpretation for pure two-slot superchannels. An immediate corollary is that purifiable bipartite processes cannot violate device-independent causal inequalities.

scholarly journals Andreev Probe of Persistent Current States in Superconducting Quantum Circuits

2005 ◽  
Vol 95 (14) ◽  
Author(s):  
V. T. Petrashov ◽  
K. G. Chua ◽  
K. M. Marshall ◽  
R. Sh. Shaikhaidarov ◽  
J. T. Nicholls
Keyword(s):  
Persistent Current ◽  
Quantum Circuits ◽  
Superconducting Quantum Circuits

scholarly journals Quantum circuits cannot control unknown operations

2014 ◽  
Vol 16 (9) ◽  
pp. 093026 ◽  
Author(s):  
Mateus Araújo ◽  
Adrien Feix ◽  
Fabio Costa ◽  
Časlav Brukner
Keyword(s):  
Quantum Circuits

scholarly journals Fully in situ Nb/InAs-nanowire Josephson junctions by selective-area growth and shadow evaporation

2021 ◽  
Author(s):  
Pujitha Perla ◽  
H. Aruni Fonseka ◽  
Patrick Zellekens ◽  
Russell Deacon ◽  
Yisong Han ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Josephson Junctions ◽  
Quantum Circuits ◽  
Selective Area Growth ◽  
Selective Area ◽  
Area Growth ◽  
Shadow Evaporation ◽  
Superconducting Quantum Circuits

Nb/InAs-nanowire Josephson junctions are fabricated in situ by a special shadow evaporation scheme for the superconducting Nb electrode. The junctions are interesting candidates for superconducting quantum circuits requiring large magnetic fields.

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