Highfidelity gate operations are essential to the realization of a faulttolerant quantum computer. In addition, the physical resources required to implement gates must scale efficiently with system size. A longstanding goal of the superconducting qubit community is the tight integration of a superconducting quantum circuit with a proximal classical cryogenic control system. Here we implement coherent control of a superconducting transmon qubit using a Single Flux Quantum (SFQ) pulse driver cofabricated on the qubit chip. The pulse driver delivers trains of quantized flux pulses to the qubit through a weak capacitive coupling; coherent rotations of the qubit state are realizedmore »
A universal quantum gate set for transmon qubits with strong ZZ interactions
Highfidelity single and twoqubit gates are essential building blocks for a faulttolerant quantum computer. While there has been much progress in suppressing singlequbit gate errors in superconducting qubit systems, twoqubit gates still suffer from error rates that are orders of magnitude higher. One limiting factor is the residual ZZinteraction, which originates from a coupling between computational states and higherenergy states. While this interaction is usually viewed as a nuisance, here we experimentally demonstrate that it can be exploited to produce a universal set of fast single and twoqubit entangling gates in a coupled transmon qubit system. To implement arbitrary singlequbit rotations, we design a new protocol called the twoaxis gate that is based on a threepart composite pulse. It rotates a single qubit independently of the state of the other qubit despite the strong ZZcoupling. We achieve singlequbit gate fidelities as high as 99.1% from randomized benchmarking measurements. We then demonstrate both a CZ gate and a CNOT gate. Because the system has a strong ZZinteraction, a CZ gate can be achieved by letting the system freely evolve for a gate time tg=53.8 ns. To design the CNOT gate, we utilize an analytical microwave pulse shape based on the SWIPHT more »
 Award ID(s):
 1839232
 Publication Date:
 NSFPAR ID:
 10297299
 Journal Name:
 ArXivorg
 Page Range or eLocationID:
 2103.12305
 ISSN:
 23318422
 Sponsoring Org:
 National Science Foundation
More Like this


Current, nearterm quantum devices have shown great progress in the last several years culminating recently with a demonstration of quantum supremacy. In the mediumterm, however, quantum machines will need to transition to greater reliability through error correction, likely through promising techniques like surface codes which are well suited for nearterm devices with limited qubit connectivity. We discover quantum memory, particularly resonant cavities with transmon qubits arranged in a 2.5D architecture, can efficiently implement surface codes with substantial hardware savings and performance/fidelity gains. Specifically, we virtualize logical qubits by storing them in layers of qubit memories connected to each transmon. Surprisingly,more »

We revisit the implementation of a twoqubit entangling gate, the MølmerSørensen gate, using the adiabatic Rydberg dressing paradigm. We study the implementation of rapid adiabatic passage using a twophoton transition, which does not require the use of an ultraviolet laser, and can be implemented using only amplitude modulation of one field with all laser frequencies fixed. We find that entangling gate fidelities, comparable to the onephoton excitation, are achievable with the twophoton excitation. Moreover, we address how the adiabatic dressing protocol can be used to implement entangling gates outside the regime of a perfect Rydberg blockade. We show that usingmore »

Current quantum computers are especially error prone and require high levels of optimization to reduce operation counts and maximize the probability the compiled program will succeed. These computers only support operations decomposed into one and twoqubit gates and only twoqubit gates between physically connected pairs of qubits. Typical compilers first decompose operations, then route data to connected qubits. We propose a new compiler structure, Orchestrated Trios, that first decomposes to the threequbit Toffoli, routes the inputs of the higherlevel Toffoli operations to groups of nearby qubits, then finishes decomposition to hardwaresupported gates. This significantly reduces communication overhead by giving themore »

The current phase of quantum computing is in the Noisy IntermediateScale Quantum (NISQ) era. On NISQ devices, twoqubit gates such as CNOTs are much noisier than singlequbit gates, so it is essential to minimize their count. Quantum circuit synthesis is a process of decomposing an arbitrary unitary into a sequence of quantum gates, and can be used as an optimization tool to produce shorter circuits to improve overall circuit fidelity. However, the timetosolution of synthesis grows exponentially with the number of qubits. As a result, synthesis is intractable for circuits on a large qubit scale. In this paper, we proposemore »