Massachusetts Institute of Technology

Andrew J Kerman

William D Oliver

Donna-Ruth Webb Yost

Danna Rosenberg

Rabindra N Das

Mark A Gouker

Karl Kimon Berggren

Eric A Dauler

Vikas Anant

Jonilyn L Yoder

Joel K W Yang

Mollie Schwartz

Wayne Woods

Thomas Hazard

Justin Mallek

Cyrus Hirjibehedin

In accordance with dissipative, photon-assisted quantum annealing described herein, a collection of qubits model a Boolean optimization problem, and the solution is determined by quantum annealing. However, rather than drive the qubits using a quasi-static field transverse to the computational direction, spins are allowed to evolve between computational states by multi-photon, inelastic collective scattering into a common waveguide coupled transversely to all of the qubits. Transitions between arbitrary states are enabled by the continuum of modes of the waveguide, while avoiding the exponential sensitivity to low-frequency decoherence near small gaps which is inherent in conventional QA. Moreover, because the transverse coupling to the waveguide averages to zero, the spin of each qubit experiences a net field purely in the computational direction, allowing continuous, quantum non-demolition measurement of the system.

Dissipative, photon-assisted quantum annealing

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 device combines physical qubits into a logical qubit according to a passive, quantum error-suppressing code, and weaves logical qubits into a fabric for performing computation or annealing according to an active, quantum error-correcting code. By using enough physical qubits in each logical qubit, the error suppression can overcome errors introduced by ambient noise, such as thermal fluctuations. However, interactions between individual logical qubits are based on interactions between multiple physical qubits, such as XX or ZZ interactions, so logical interactions require intermediary circuitry capable of coupling four or more spins-this circuitry also is described, wherein coupling an ancilla qubit to such intermediary circuitry allows the formation of a logical qubit having passive error suppression, and arbitrary computations can be performed using a fabric of such circuitry. Concatenating the active and passive codes does not increase circuit complexity, or reduce the speed of gate operations.

Physical-layer quantum error suppression for superconducting qubits in quantum computation and optimization

A qubit includes a superconducting loop interrupted by a plurality of magnetic flux tunneling elements, such as DC SQUIDs, leaving superconducting islands between the elements. An effective transverse magnetic moment is formed by magnetically tuning each element to yield a large tunneling amplitude. The electrical polarization charge on an island is tuned to produce destructive interference between the tunneling amplitudes using the Aharonov-Casher effect, resulting in an effectively zero transverse field. Biasing the charge away from this tuning allows tunneling to resume with a large amplitude. Interrupting the island with a third tunneling path, such as a Josephson junction, permits independently tuning and biasing the two islands that result, enabling effective control of two independent (X and Y) transverse fields.

Josephson phase-slip qubits

Described herein are structures and techniques for highly-connected qubit interaction using a 'paramagnetic tree coupling' scheme. In one embodiment, a structure for providing highly-connected qubit interaction includes a plurality of qubits and, for each of the plurality of qubits, a paramagnetic medium connecting the qubit to each other one of the plurality of qubits, where the paramagnetic medium includes a series of inductive couplers.

Paramagnetic tree coupling of spin qubits

Structures and techniques, using superconducting Josephson-junction based circuits, to directly engineer physical multiqubit (or 'many-qubit') interactions in a non-perturbative manner. In one embodiment, a system for multiqubit interaction includes: a multispin coupler including a plurality of loops, each loop having a pair of Josephson junctions; and a plurality of qubits each inductively coupled to the multispin coupler.

Four spin couplers for quantum information processing

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

Multiloop interferometers for quantum information processing

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 multi-element optical detector includes a plurality of optical detector elements capable of producing an output signal having information about the state of an incident electromagnetic radiation as a function of time. An active region includes a photosensitive region of one of the optical detector elements separated in part or in whole from the photosensitive region of at least one other optical detector element by a distance less than the wavelength of the electromagnetic radiation that the optical detector elements are being used to detect.

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Arlington, MA, United States of America

Andrew J Kerman