Convex optimization of programmable quantum computers

  title={Convex optimization of programmable quantum computers},
  author={Leonardo Banchi and Jason L. Pereira and Seth Lloyd and Stefano Pirandola},
  journal={npj Quantum Information},
A fundamental model of quantum computation is the programmable quantum gate array. This is a quantum processor that is fed by a program state that induces a corresponding quantum operation on input states. While being programmable, any finite-dimensional design of this model is known to be nonuniversal, meaning that the processor cannot perfectly simulate an arbitrary quantum channel over the input. Characterizing how close the simulation is and finding the optimal program state have been open… 
Programmability of covariant quantum channels
By leveraging the representation theory of the symmetry group action, it is shown how to remove redundancy in the program and proved that the resulting program register has minimum Hilbert space dimension.
Fundamental limitations on distillation of quantum channel resources
This work establishes universal limitations on the processing of both quantum states and channels, expressed in the form of no-go theorems and quantitative bounds for the manipulation of general quantum channel resources under the most general transformation protocols.
Machine Learning: Quantum vs Classical
An overview of quantum machine learning in the light of classical approaches is presented, discussing various technical contributions, strengths and similarities of the research work in this domain and elaborate upon the recent progress of different quantum machinelearning approaches, their complexity, and applications in various fields such as physics, chemistry and natural language processing.
No-Go Theorems for Quantum Resource Purification: New Approach and Channel Theory
A novel and powerful method is developed for analyzing the limitations of quantum resource purification, which not only leads to improved bounds that rule out exact purification for a broader range of noisy states and are tight in certain cases, but also allow us to establish a no-purification theory for quantum channel (dynamical) resources.
Multiport based teleportation – transmission of a large amount of quantum information
The obtained bound is effectively computable and outperforms the explicit values of the entanglement fidelity calculated for the pre-existing variants of the port-based protocols, allowing for teleportation of a much larger amount of quantum information.
Fundamental limitations on quantum channel manipulation
Comprehensive lower bounds for the overhead of any physical distillation protocol in terms of required channel uses are introduced, imposing strong limitations on the practical efficiency and cost of channel manipulation protocols.
Mixed state entanglement classification using artificial neural networks
The use of separable neural network quantum states is extended to mixed, multipartite states, providing a versatile and efficient tool for the investigation of intricately entangled quantum systems.
Advances in Quantum Cryptography
This review begins by reviewing protocols of quantum key distribution based on discrete variable systems, and considers aspects of device independence, satellite challenges, and high rate protocols based on continuous variable systems.
Ultimate Limits for Multiple Quantum Channel Discrimination.
This Letter establishes a lower limit for the ultimate error probability affecting the discrimination of an arbitrary number of quantum channels, and shows that this lower bound is achievable when the channels have certain symmetries.


Optimization and learning of quantum programs
This work proves that the search for the optimal quantum program is a convex optimization problem, and applies this general result to a number of different designs for the programmable quantum processor, from the shallow protocol of quantum teleportation, to deeper schemes relying on port-based teleportation and parametric quantum circuits.
4 – Quantum Computing
Quantum circuit learning
A classical-quantum hybrid algorithm for machine learning on near-term quantum processors, which is hybridizing a low-depth quantum circuit and a classical computer for machinelearning, paves the way toward applications of near- term quantum devices for quantum machine learning.
Quantum gate learning in qubit networks: Toffoli gate without time-dependent control
Researchers have developed a strategy for performing operations in quantum computing networks without requiring external control input. Although quantum algorithms offer the benefit of faster
Programmable Quantum Gate Arrays
It is shown that a universal quantum gate array which can be programmed to perform any unitary operation exists only if one allows the gate array to operate in a probabilistic fashion, and that it is not possible to build a fixed, general purpose quantum computer which can been programmed to Perform an arbitrary quantum computation.
Efficient universal programmable quantum measurements.
This Letter shows that, much better than the exponential size known in the literature, one can achieve polynomial size and shows that for covariant measurements exact programmability is feasible.
Machine learning method for state preparation and gate synthesis on photonic quantum computers
Techniques from machine learning and optimization can be used to find circuits of photonic quantum computers that perform a desired transformation between input and output states, and obtains circuits that reproduce the action of a target unitary transformation.
Fundamental limits to quantum channel discrimination
This work investigates the symmetric discrimination of two arbitrary qudit channels by means of the most general protocols based on adaptive (feedback-assisted) quantum operations, and derives ultimate limits and no-go theorems for adaptive quantum illumination and single-photon quantum optical resolution.
A scheme for efficient quantum computation with linear optics
It is shown that efficient quantum computation is possible using only beam splitters, phase shifters, single photon sources and photo-detectors and are robust against errors from photon loss and detector inefficiency.
General Benchmarks for Quantum Repeaters
Using a technique based on quantum teleportation, we simplify the most general adaptive protocols for key distribution, entanglement distillation and quantum communication over a wide class of