Towards Fault-Tolerance in a Hardware-Efficient Modular Architecture
Abstract
We propose to fully develop our modular architecture paradigm for quantum computation based on circuit QED. Many groups are attempting to Ôscale up and then error correct.Õ We argue that the opposite approach, Ôerror correct and then scale up,Õ is far superior and vastly more hardware efficient. Using this approach, we have recently demonstrated logical qubits with quantum error correction that reaches the break-even point for the first time in any hardware platform. Our logical qubits use error-correctable bosonic codes (e.g. the cat code or binomial codes) consisting of coherent superpositions of small numbers of photons stored in microwave resonators. We will use our simple and robust logical qubits to develop and demonstrate universal gates on two logical qubits based on a new Ôcontrolled swapÕ protocol. We already have preliminary techniques using an ancilla transmon qubit to carry out one- and two-qubit gates at the logical encoding level. We will fully develop and expand these and make the system more fault-tolerant with respect to transmon errors by introducing a new strategy that requires no additional hardware. This is a first instance of our new concept for incorporating fault tolerance in a hardware-efficient manner, which will be extended and explored in this proposal. We will develop these techniques and use them to improve the efficiency of quantum error correction and achieve the target for gate infidelities ( ? 10-2). Our logical qubits are exceptionally hardware-efficient because microwave resonators have a large Hilbert space, are naturally robust against off-resonant noise, and have a very simple amplitude- damping error model with naturally low error rate. Furthermore, full quantum control, error correction and full state/process tomography can be performed with only a single ancilla transmon and a single microwave control/readout channel. This remarkable efficiency will allow us to develop a practical design path to a 10-logical-qubit modular device capable of carrying out non- trivial algorithms of interest. In addition, we will advance new methods in which all errors arising from photon losses will be corrected continuously and autonomously: the continuous energy losses of the encoded states will be corrected by a form of Ôcat pumpingÕ while the discrete jumps of parity will be corrected by an autonomous feedback scheme similar to the method we have previously used to stabilize an entangled state. The strong photon-transmon coupling in circuit QED makes it possible to carry out operations that are conditioned on the state of bosonic logical qubits or ancilla transmon qubits. We will work to develop quantum-controlled linear optical transformations that have the advantage of being agnostic as to the photonic code words being used and yield great flexibility to utilize different encodings on the same hardware to optimize operation of each layer of the hardware stack. Our modular circuit QED implementation could thus be used to realize the novel and powerful Lau and Plenio scheme for universal quantum computing with arbitrary continuous-variable encoding.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 25, 2019
- Source ID
- W911NF1810212
Entities
People
- Steven Girvin
Organizations
- Army Contracting Command
- National Security Agency
- Yale University