Massachusetts Institute of Technology

Rtx Bbn Technologies, Inc.

Socpra Sciences Et Genie S.e.c., A/s Transfertech Sherbrooke

William D Oliver

Danna Rosenberg

Rabindra N Das

Andrew J Kerman

Donna-Ruth Webb Yost

Mark A Gouker

Simon Gustavsson

Antti Pekka Vepsalainen

Alexandre Blais

Terry Philip Orlando

Roni Winik

Mollie Schwartz

Jonilyn L Yoder

Thomas Ohki

Hari Kiran Krovi

Vladimir Bolkhovsky

Seth Lloyd

Michael F O'Keeffe

Luke Colin Gene Govia

David J Hover

Wayne Woods

Iman Marvian Mashhad

Gabriel Samach

Morten Kjaergaard

Amy Greene

Benjamin Lienhard

Agustin Di Paolo

Mark S Rudner

I-Jan Wang

Sergio O Valenzuela

Leonid S Levitov

Corey W Stull

Catherine Leroux

Xhovalin Miloshi

Thomas Hazard

David M Berns

Youngku Sung

Jochen Braumueller

Justin Mallek

Cyrus Hirjibehedin

A system and method provide two-qubit gates and quantum computing circuits built therefrom. Pairs of qubits are inductively or capacitively coupled using a coupler that is driven using an off-resonant microwave drive. By controlling the drive, the ZZ interaction between the qubits can be precisely controlled. In particular, the interaction may be selectively reduced or suppressed, thereby isolating the qubits from each other, or the interaction may be increased to provide fast, controlled-Z, two-qubit gates with high fidelity. Moreover, qubits and couplers may be arranged according to their resonant frequencies into unit cells and replicated to arbitrary size, thereby forming a quantum computer.

Tunable interactions for implementing two-qubit gates, and extensible circuits built therefrom

Techniques for machine learning assisted qubit state readout are disclosed. A system a set of training data that describes states of multiple qubits, and trains a neural network to determine qubit states based on the set of training data. The system obtains one or more unlabeled qubit signals, and determines one or more states corresponding to the unlabeled qubit signal(s), using the neural network. The unlabeled qubit signal(s) may include one or more multiplexed qubit signals, and the state(s) corresponding to the unlabeled qubit signal(s) may include one or more multi-qubit states based on the multiplexed qubit signal(s).

Machine learning assisted qubit state readout

Systems and methods for performing open-loop quantum error mitigation using quantum measurement emulations are provided. The open-loop quantum error mitigation methods do not require the performance of state readouts or state tomography, reducing hardware requirements and increasing overall computation speed. To perform a quantum measurement emulation, an error mitigation apparatus is configured to stochastically apply a quantum gate to a qubit or set of qubits during a quantum computational process. The stochastic application of the quantum gate projects the quantum state of the affected qubits onto an axis, reducing a trace distance between the quantum state and a desired quantum state.

Quantum measurement emulation error mitigation protocol for quantum computing

Qubit circuits having components formed deep in a substrate are described. The qubit circuits can be manufactured using existing integrated-circuit technologies. By forming components such as superconducting current loops, inductive, and/or capacitive components deep in the substrate, the footprint of the qubit circuit integrated within the substrate can be reduced. Additionally, coupling efficiency to and from the qubit can be improved and losses in the qubit circuit may be reduced.

Qubit circuits with deep, in-substrate components

A closed-loop feedback system and method of active noise cancellation to maintain a desired operating frequency of a qubit during a quantum computation, even when that frequency is relatively sensitive to flux noise. A series of Ramsey experiments is performed on the qubit to estimate an offset between its actual and desired operating frequencies, and the error is accumulated. After the probing is complete, the accumulated error is supplied to an arbitrary waveform generator that produces a magnetic flux that is coupled to the qubit, thereby tuning the qubit and actively controlling its operating frequency. Having corrected the operating frequency of the qubit and extended its coherence time, the quantum state of the qubit is allowed to evolve according to the computation.

Active noise cancelation in superconducting Qubits using closed-loop feedback

A quantum circuit called a 'qumon' is provided to cancel unwanted ZZ interaction in a superconducting qubit architecture. The qumon qubit has a high coherence, and a positive anharmonicity that may be tuned to cancel the negative anharmonicity in a coupled qubit, such as a transmon qubit. The qumon has three parallel branches, in which are a shunt capacitor; a Josephson junction having weighted energy level and capacitance; and several Josephson junctions in series. The weight is chosen to provide the desired anharmonicity, and the transverse flux noise and transverse charge noise each decrease in proportion to the number of the Josephson junctions in series. Because unwanted ZZ interactions are canceled, qumon qubits and transmon qubits may be capacitively coupled in an alternating pattern to provide a surface code in which these interactions are canceled in an extensible way.

Cancellation of unwanted interactions in a superconducting quantum architecture

According to some embodiments, a method can identify and discriminate contributions from one or more noise sources using the multi-level structure of a quantum system with three or more levels. The method can include: preparing the quantum system in a predetermined state; applying one or more control signals to the quantum system; measuring values of one or more observables of the quantum system that quantify the quantum system's response to the noise sources and the one or more applied control signals; extracting noise spectra information associated with the noise sources from the measured values; and identifying contributions from the one or more noise sources based on the noise spectra information.

Identifying noise sources in quantum systems via multi-level noise spectroscopy

A superconducting qubit is manufactured by stacking up atomically-thin, crystalline monolayers to form a heterostructure held together by van der Waals forces. Two sheets of superconducting material are separated by a third, thin sheet of dielectric to provide both a parallel plate shunting capacitor and a Josephson tunneling barrier. The superconducting material may be a transition metal dichalcogenide (TMD), such as niobium disilicate, and the dielectric may be hexagonal boron nitride. The qubit is etched, or material otherwise removed, to form a magnetic flux loop for tuning. The heterostructure may be protected by adhering additional layers of the dielectric or other insulator on its top and bottom. For readout, the qubit may be coupled to an external resonator, or the resonator may be integral with one of the sheets of superconducting material.

High coherence, small footprint superconducting qubit made by stacking up atomically thin crystals

A superconducting integrated circuit includes at least one superconducting resonator, including a substrate, a conductive layer disposed over a surface of the substrate with the conductive layer including at least one conductive material including a substantially low stress polycrystalline Titanium Nitride (TiN) material having an internal stress less than about two hundred fifty MPa (magnitude) such that the at least one superconducting resonator and/or qubit (hereafter called 'device') is provided as a substantially high quality factor, low loss superconducting device.

Superconducting integrated circuit

A multi-layer semiconductor structure includes a first semiconductor structure and a second semiconductor structure, with at least one of the first and second semiconductor structures provided as a superconducting semiconductor structure. The multi-layer semiconductor structure also includes one or more interconnect structures. Each of the interconnect structures is disposed between the first and second semiconductor structures and coupled to respective ones of interconnect pads provided on the first and second semiconductor structures. Additionally, each of the interconnect structures includes a plurality of interconnect sections. At least one of the interconnect sections includes at least one superconducting and/or a partially superconducting material.

Interconnect structures for assembly of semiconductor structures including superconducting integrated circuits

Described are concepts, systems, circuits and techniques related to shielded through via structures and methods for fabricating such shielded through via structures. The described shielded through via structures and techniques allow for assembly of multi-layer semiconductor structures including one or more superconducting semiconductor structures (or integrated circuits).

Shielded through via structures and methods for fabricating shielded through via structures

A cryogenic quantum bit package with multiple qubit circuits facilitates inter-qubit signal propagation using a multi-chip module (MCM). Multiple qubits are grouped within the package into one or more qubit integrated circuits (ICs). The qubit ICs themselves are electrically coupled to each other via a structure including a superconducting MCM and superconducting interconnects. Coupling of quantum electrical signals between a qubit and other qubits, a substrate, or the MCM uses a coupler circuit, such as a Josephson junction, capacitor, inductor, or resonator.

Qubit and coupler circuit structures and coupling techniques

A method of fabricating an interconnect structure includes providing a semiconductor structure and performing a first spin resist and bake cycle. The first spin resist and bake cycle includes applying a first predetermined amount of a resist material over one or more portions of the semiconductor structure and baking the semiconductor structure to form a first resist layer portion of a resist layer. The method also includes performing a next spin resist and bake cycle. The next spin resist and bake cycle includes applying a next predetermined amount of the resist material and baking the semiconductor structure to form a next resist layer portion of the resist layer. The method additionally includes depositing a conductive material in an opening formed in the resist layer and forming a conductive structure from the conductive material. An interconnect structure is also provided.

Interconnect structures and methods for fabricating interconnect structures

A system and method for providing amplitude spectroscopy is provided. Generally, the system contains a generator for providing a waveform for analysis of a multilevel quantum system, wherein the generator has the capability of changing amplitude of the waveform provided and driving the multilevel quantum system at a fixed frequency while sweeping amplitude. A detector is also provided for reading population in different energy states of the multilevel quantum system, wherein the detector plots an amplitude spectroscopy response of the multilevel quantum system. A memory and processor are provided within the system where the processor is configured by the memory to perform the step of plotting an energy-level diagram of the multilevel quantum system from the amplitude spectroscopy plot of the multilevel quantum system.

System and method for providing amplitude spectroscopy of a multilevel quantum system

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Arlington, MA, United States of America

William D Oliver