# VTQ Research Areas

## Quantum Computing

VTQ researchers are working on quantum computing along a number of directions. These include the design of logical gate operations and quantum processor architectures for several different quantum computing platforms, including superconducting circuits, semiconductor spins, and more. Suppressing decoherence, error mitigation, and quantum error correction are important aspects of quantum computing research in the center. VTQ is also involved in the development of new types of qubits, coupling mechanisms, quantum processor device components, and so on, using a combination of ab initio modeling and multi-qubit dynamics simulations. In addition to circuit-based approaches, VTQ also investigates measurement-based quantum computing in which computations are carried out starting from large, multi-qubit entangled states such as graph states or cluster states and then performing single-qubit measurements. This research includes developing schemes to efficiently create entanglement between large numbers of photonic qubits produced from quantum emitters. In addition, VTQ quantum computing research involves the development of quantum algorithms for optimization problems and for simulating complex quantum systems, as well as the study of existing algorithms and finding ways to improve their performance.

** Related Faculty: **
Ed Barnes
,
Charles Cao
,
Sophia Economou
,
Nick Mayhall
,
Kyungwha Park
,
Vito Scarola
,
Jamie Sikora
,
Linbo Shao
.

## Quantum Simulation

While the simulation of quantum systems on today's classical computers has been tremendously successful, large, strongly correlated quantum systems remain challenging even for the world's best supercomputers. This is due to the inability of classical machines to efficiently store or manipulate exponentially large quantum states. The concept of quantum simulation proposes to circumvent this problem by replacing or supplementing the classical computer with a programmable quantum processor built from qubits. Quantum simulation is believed to be one of the most near-term applications of quantum information science in that a modest-sized quantum processor containing as few as 50-100 qubits may be sufficient to simulate systems that are classically intractable. Realizing this potential requires simultaneous advancements in qubit hardware and in simulation algorithms. Our research focuses on developing new, efficient algorithms for quantum simulation that reduce the required quantum resources. VTQ researchers also work closely with experimental groups to determine the control schemes and device architectures that are optimal for achieving efficient, accurate simulations.

** Related Faculty: **
Nick Mayhall
,
Sophia Economou
,
Ed Barnes
,
Vito Scarola
.

## Quantum Communication

Future powerful quantum computers will be capable of running algorithms that can be used to crack the RSA encryption system---the predominant scheme used to protect internet transactions across the world. Although quantum mechanics can be used to compromise information security in this way, it also offers a way to defend against such attacks. The quantum no-cloning theorem, which forbids the copying of unknown quantum states, implies that it is possible to transmit information in a way that makes it impossible to intercept transmissions without being detected. This idea has lead to the notion of quantum communication, which aims to develop communication networks that are immune to hacking, even by large-scale quantum computers. While the no-cloning theorem is the basic principle that makes quantum communication possible, it also poses a challenge. Transmitting information over long distances generally requires that the information be copied and re-amplified at multiple points (repeaters) along the information path due to the lossiness of optical fibers. However, the no-cloning theorem prevents a direct implementation of this idea in the case of quantum information. Quantum entanglement can be used to get around this problem. VTQ researchers are developing schemes to produce complex, entangled states of light for long-distance quantum communication networks, to characterize quantum network performance, and to develop new cryptographic protocols, including quantum and post-quantum approaches.

** Related Faculty: **
Sophia Economou
,
Ed Barnes
,
Jamie Sikora
,
Atul Mantri
,
Gretchen Matthews
.

## Quantum entanglement, many-body dynamics, and error correction

In addition to being a uniquely quantum concept that has no classical analog, quantum entanglement is also a fundamental resource for most quantum information technologies. Large-scale many-body (or multi-qubit) entanglement is especially important for quantum network applications, measurement-based quantum computing, and quantum error correction. This is why it is important to understand how many-body entanglement can be created and how it evolves over time. It is also important to understand how entanglement is affected by measurements and other factors that arise in quantum computation. In addition to serving as a QISE resource, entanglement can also be used to characterize and distinguish different types of dynamical many-body systems. Thus, questions related to the growth and spread of entanglement naturally lie at the interface of QISE and quantum condensed matter physics. VTQ researchers are working to shed light on these issues with the aim of both improving our fundamental understanding of entanglement and of learning how to best leverage it for practical applications. One of the most important applications is quantum error correction. As in classical computation, logical gate operations on quantum devices are prone to errors, limiting the scale of computations that can be done accurately. VTQ researchers are working to develop new quantum error correction codes that substantially lower the cost of implementing error correction to bring the era of fault-tolerant quantum computing closer to the present.

** Related Faculty: **
Tianci Zhou
,
Charles Cao
,
Ed Barnes
,
Sophia Economou
,
Vito Scarola
.