RQS Seminar

Error-mitigation techniques can enable access to accurate estimates of physical observables that are otherwise biased by noise in pre-fault-tolerant quantum computers. One particularly general error-mitigation technique is probabilistic error cancellation (PEC), which effectively inverts a well-characterized noise channel to produce noise-free estimates of observables. Experimental realizations of this technique, however, have been impeded by the challenge of learning correlated noise in large quantum circuits.

In recent years, there have been rapid breakthroughs in quantum technologies that offer new opportunities for advancing the understanding of basic quantum phenomena; realizing novel strongly correlated systems; and enhancing applications in quantum communication, computation, and sensing. Cutting edge quantum technologies simultaneously require high fidelity quantum-limited measurements and control. Large-scale applications of these capabilities hinge on understanding system-reservoir dynamics of many-body quantum systems, whose Hilbert space grows exponentially with system size.

Previous work by Brakerski et al. (2018) described a 2-party interactive protocol that enables one party to prove that they have quantum computational abilities. The protocol is based on the Learning With Errors (LWE) assumption, a standard computational hardness assumption from classical cryptography. In this talk, I will give an introduction to the protocol of Brakerski et al., and then I will discuss a recent paper of ours that optimizes their protocol and brings it closer to experimental realization.

Quantum computers offer the potential to perform simulations of nuclear processes that are infeasible for classical devices. With a goal of understanding the necessary quantum resources to realize such potential, we estimate the qubit costs and gate costs to simulate an effective nuclear field theory on a cubic lattice, evaluating the various trade-offs in choice of the form of the effective field theory and how this choice interacts with the qubit requirements of encoding the fermionic degrees of freedom into qubits and the gate counts needed for state-of-the-art Hamiltonian simulation.

The central philosophy of statistical mechanics and random-matrix theory of complex systems is that while individual instances are essentially intractable to simulate, the statistical properties of random ensembles obey simple universal “laws”. This same philosophy promises powerful methods for studying the dynamics of quantum information in ideal and noisy quantum circuits – for which classical description of individual circuits is expected to be generically intractable.

Near-term quantum information processors will not be capable of quantum error correction, but instead will implement algorithms using the physical native interactions of the device. These interactions can be used to implement quantum gates that are often continuously-parameterized (e.g., by rotation angles), as well as to implement analog quantum simulations that seek to explore the dynamics of a particular Hamiltonian of interest.

Real-time control software and hardware is essential for operating modern quantum systems. In particular, the software plays a crucial role in bridging the gap between applications and real-time operations on the quantum system. Unfortunately, real-time control software is an often underexposed area, and many well-known software engineering techniques have not propagated to this field. As a result, control software is often hardware-specific at the cost of flexibility and portability.

Analog quantum simulators have the potential to provide new insight towards naturally occurring phenomena beyond the capabilities of classical computers in the near term. Incorporating controllable dissipation as a resource enables simulation of a wider range of out-of-equilibrium processes such as chemical reactions. In this talk, I will describe an experiment where we operate a hybrid qubit-oscillator circuit quantum electrodynamics processor and use it to model nonadiabatic molecular reaction dynamics through a so-called conical intersection.