Quantum simulation of dissipative collective effects on noisy quantum computers

Abstract

Dissipative collective effects are ubiquitous in quantum physics, and their relevance ranges from the study of entanglement in biological systems to noise mitigation in quantum computers. Here, we put forward the first fully quantum simulation of dissipative collective phenomena on a real quantum computer. The quantum simulation is based on the recently introduced multipartite collision model, which reproduces the action of a dissipative common environment by means of repeated interactions between the system and some ancillary qubits. First, we theoretically study the accuracy of this algorithm on near-term quantum computers with noisy gates, and we derive some rigorous error bounds which depend on the timestep of the collision model and on the gate errors. These bounds can be employed to estimate the necessary resources for the efficient quantum simulation of the collective dynamics. Then, we implement the algorithm on some IBM quantum computers to simulate superradiance and subradiance between a pair of qubits. Our experimental results successfully display the emergence of collective effects in the quantum simulation. Finally, we analyze the noise properties of the gates we employed in the algorithm by means of full process tomography. Using the state-of-the-art tools for noise analysis in quantum computers, we obtain the values of the average gate fidelity, unitarity and diamond error, and we establish a connection between them and the accuracy of the experimentally simulated state. Although the scaling of the error as a function of the number of gates is favorable, we observe that reaching the threshold for quantum fault tolerant computation is still orders of magnitude away.

Exploiting coherence for quantum thermodynamic advantage

“…Implementing our proposal in current experiments could face critical technical challenges such as scaling, decoherence and manufacturing errors. Nonetheless, the first proof-of-principle demonstrations have already shown great potential for future thermodynamic applications [81,83,84].…”

“…The basic formulation of CMs consists of depicting the environment as a large ensemble of elementary components or sub-units, often called ancillas, that interact sequentially with a system S. The system-ancilla joint dynamics are described by collisions that may or may not preserve energy. The conditions for a memoryless Markovian behaviour of the open quantum system evolution imply that the ancillas are initially prepared in a product state (uncorrelated) and that every ancilla collides only once with S. In addition to being an interesting asset to study non-thermal environments, this microscopic formalism is highly suited to model specific experiments based on micromasers [78,79], nuclear magnetic resonance (NMR) [80], superconducting quantum computers [81][82][83][84] and all-optical settings [85][86][87].…”

Quantum State Preparation and Non-Unitary Evolution with Diagonal Operators

“…Current quantum devices are typically unitary-gate-based, so non-unitary operators must be cast as unitary in order to be practically implementable. There are a variety of algorithms which have been developed to bypass this obstacle, including explicit mathematical dilations [8][9][10][11][12][13][14], quantum imaginary time evolution [15], duality [16,17], the variational principal [18], collision models [19], analog simulation [20], and others [21][22][23][24][25][26][27][28][29][30][31][32]. The majority of these algorithms rely on some form of dilation, either mapping the operator to a larger Hilbert space, or adding ancilla qubits.…”