Superconducting Qubits: Current State of Play

Abstract

Superconducting qubits are leading candidates in the race to build a quantum computer capable of realizing computations beyond the reach of modern supercomputers. The superconducting qubit modality has been used to demonstrate prototype algorithms in the 'noisy intermediate scale quantum' (NISQ) technology era, in which non-error-corrected qubits are used to implement quantum simulations and quantum algorithms. With the recent demonstrations of multiple high fidelity two-qubit gates as well as operations on logical qubits in extensible superconducting qubit systems, this modality also holds promise for the longer-term goal of building larger-scale error-corrected quantum computers. In this brief review, we discuss several of the recent experimental advances in qubit hardware, gate implementations, readout capabilities, early NISQ algorithm implementations, and quantum error correction using superconducting qubits. While continued work on many aspects of this technology is certainly necessary, the pace of both conceptual and technical progress in the last years has been impressive, and here we hope to convey the excitement stemming from this progress.

Quantum Decoherence in Dense Media: A Few Examples

“…Improvements have been introduced by adding parallel circuits containing additional Josephson junctions (transmon circuits), which assist in further separating the lowest qubit states |0> and |1> energetically and increasing their stability, and also by coupling the qubits to high Q-photon cavities instead of classical microwave sources (referred to as circuit QED [31]). Continued improvement in the coherence times up to  coh = 10 -4 s was demonstrated in a recent study conducted by Kjaergaard et al [32]. The remaining sources for decoherence are stray capacitances and local defects related to difficulties in the fabrication of small-size superconducting islands and Josephson junctions ( Figure 12).…”

Realizing Quantum Algorithms on Real Quantum Computing Devices

“…In the introduction we mentioned that multiple physical implementation of quantum processors are currently developed, including but not limited to trapped ions, silicon quantum dots, photonics, neutral atoms, and topological systems. The maturity of each technology is at a di erent point and the challenges to scalability are also di erent [4]- [7]. Here we are interested to provide a few examples in which particular physical implementations provide unique features.…”

“…By exploiting quantum phenomena such as superposition and entanglement, quantum computers promise to solve hard problems that are intractable for even the most powerful conventional supercomputers. In addition, remarkable progress has been made in quantum hardware based on di erent technologies such as superconducting circuits, trapped ions, silicon quantum dots, and topological qubits [4]- [7]. A recent breakthrough in quantum computing has been the experimental demonstration of quantum supremacy 1 using a superconducting quantum processor consisting of 53 qubits [8].…”

A quantum-classical cloud platform optimized for variational hybrid algorithms

“…These algorithms have been applied to areas such as combinatorial optimization [26,46], quantum chemistry [47,45], and machine learning [57], and numerous proposals for applications of the variational method continue to arise with increasing frequency [17,55]. However, VHAs require a tight coupling between quantum and classical resources, and using a cloud-hosted queue is slow with respect to the scale of quantum operations, especially on a superconducting device [35]. In addition, a quantum cloud architecture must be specifically optimized in order to efficiently support the variational model of execution.…”