Abstract: The present application describes a waveform processor for control of quantum mechanical systems. The waveform processor may be used to control quantum systems used in quantum computation, such as qubits. According to some embodiments, a waveform processor includes a first sequencer configured to sequentially execute master instructions according to a defined order and output digital values in response to the executed master instructions, and a second sequencer coupled to the first sequencer and configured to generate analog waveforms at least in part by transforming digital waveforms according to digital values received from the first sequencer. The analog waveforms are applied to a quantum system. In some embodiments, the waveform processor further includes a waveform analyzer configured to integrate analog waveforms received from a quantum system and output results of said integration to the first sequencer.

Abstract: Techniques for implementing robust quantum logic gates are provided and described. In some aspects, a quantum logic gate between a plurality of cavities comprising a first cavity and a second cavity is implemented by performing a first beam splitter operation between the first cavity and the second cavity using a coupling transmon that is dispersively coupled to both the first cavity and the second cavity, and performing a controlled phase shift operation between the second cavity and an ancilla transmon that is dispersively coupled to the second cavity but not dispersively coupled to the first cavity.

Abstract: Techniques for providing hardware-efficient fault-tolerant quantum operations are provided. In some aspects a cavity and an ancilla transmon are used to implement a quantum operation by encoding a logical qubit using more than two energy levels of the cavity, encoding information using more than two energy levels of the ancilla transmon, and creating an interaction between the cavity and the ancilla transmon that decouples at least one error type in the ancilla transmon from the cavity.

Abstract: Techniques for implementing a QRAM by routing quantum information through multiple modes of a bosonic system are described. According to some aspects, a single bosonic system may be configured to maintain quantum information in a large number of independent modes at the same time. Suitable operations upon these modes may allow a quantum address value to be routed to modes associated with respective bits such that the only modes altered by the operations are those associated with the addresses being accessed. These modes may be operated upon based on the stored values then extracted to obtain the desired correlated superposition of the stored bit values in the addresses. The bits stored at the address locations may be classical bits, or may be qubits.

Abstract: A wireless Josephson-junction-based amplifier is described that provides improved tunability and increased control over both a quality factor Q and participation ratio p of the amplifier. The device may be fabricated on a chip and mounted in a waveguide. No wire bonding between the amplifier and coaxial cables or a printed circuit board is needed. At least one antenna on the chip may be used to couple energy between the waveguide and wireless JBA. The amplifier is capable of gains greater than 25 dB.

Abstract: Techniques are described in which a qubit is far off-resonantly, or dispersively, coupled to a quantum mechanical oscillator. In particular, a dispersive coupling between a physical qubit and a quantum mechanical oscillator may be selected such that control of the combined qubit-oscillator system can be realized. The physical qubit may be driven with an electromagnetic pulse (e.g., a microwave pulse) and the quantum mechanical oscillator simultaneously driven with another electromagnetic pulse, the combination of which results in a change in state of the qubit-oscillator system.

Abstract: According to some aspects, a method is provided of operating a system that includes a multi-level quantum system dispersively coupled to a first quantum mechanical oscillator and dispersively coupled to a second quantum mechanical oscillator, the method comprising applying a first drive waveform to the multi-level quantum system, applying one or more second drive waveforms to the first quantum mechanical oscillator, and applying one or more third drive waveforms to the second quantum mechanical oscillator.

Abstract: Some aspects are directed to a method of operating an apparatus, the apparatus comprising a first quantum system having a plurality of coherent quantum states, the first quantum system being coupled to a second quantum system, the method comprising providing an input energy signal to the second quantum system that stimulates energy transfer between the first quantum system and the second quantum system and that causes net dissipation of energy to be output from the second quantum system, wherein the input energy signal includes at least two components having different frequencies and each having an amplitude and a phase, and adiabatically varying the amplitude and the phase of the at least two components of the input energy signal to cause a change in one or more of the plurality of coherent quantum states of the first quantum system.

Abstract: Techniques for operating a mechanical oscillator as a quantum memory are described. According to some aspects, a qubit may be coupled to a piezoelectric material such that the electric field of the qubit causes stress within the piezoelectric material. The piezoelectric material may be in contact with a crystalline substrate forming an acoustic resonator such that the qubit couples to bulk acoustic waves in the crystalline substrate via its interaction with the piezoelectric material. According to some aspects, application of a suitable electromagnetic pulse to the qubit may cause an exchange of energy from the qubit to the acoustic phonon system and thereby transfer quantum information from the qubit to the phonon system.

Abstract: Techniques for providing hardware-efficient fault-tolerant quantum operations are provided. In some aspects a cavity and an ancilla transmon are used to implement a quantum operation by encoding a logical qubit using more than two energy levels of the cavity, encoding information using more than two energy levels of the ancilla transmon, and creating an interaction between the cavity and the ancilla transmon that decouples at least one error type in the ancilla transmon from the cavity.

Abstract: According to some aspects, a quantum information system is provided that includes an ancilla qubit; a qudit coupled to the ancilla qubit, a detector configured to generate a detection result based on a quantum state of the ancilla qubit, and a driving source coupled to the qudit and the ancilla qubit and configured to apply at least one qudit driving signal to the qudit based on the detection result and at least one qubit driving signal to the qudit based on the detection result.

Abstract: Techniques for operating a mechanical oscillator as a quantum memory are described. According to some aspects, a qubit may be coupled to a piezoelectric material such that the electric field of the qubit causes stress within the piezoelectric material. The piezoelectric material may be in contact with a crystalline substrate forming an acoustic resonator such that the qubit couples to bulk acoustic waves in the crystalline substrate via its interaction with the suitable electromagnetic pulse to the qubit may cause an exchange of energy from the qubit to the acoustic phonon system and thereby transfer quantum information from the qubit to the phonon system.

Abstract: A wireless Josephson-junction-based parametric converter is described. The converter may be formed on a substrate with antennas that pump are configured to wirelessly receive pump, signal and idler frequencies and couple the received frequencies to the converter's circuitry. Capacitors may also be fabricated on the same substrate and sized to tune operation of the converter to desired frequencies. The converter may be coupled directly to microwave waveguides, and may be tuned to different signal frequencies by applying magnetic flux to the converter circuitry.

Abstract: According to some aspects, a method is provided of operating a circuit quantum electrodynamics system that includes a physical qubit dispersively coupled to a quantum mechanical oscillator, the method comprising applying a first electromagnetic pulse to the physical qubit based on a number state of the quantum mechanical oscillator, wherein the first electromagnetic pulse causes a change in state of the quantum mechanical oscillator, and applying, subsequent to application of the first electromagnetic pulse, a second electromagnetic pulse to the quantum mechanical oscillator that coherently adds or removes energy from the quantum mechanical oscillator.

Abstract: A low-noise directional amplifier includes a first port, a second port, a first coupler and a second coupler. The first port is coupled to a first coupler. The low-noise directional amplifier also includes at least two phase preserving amplifiers, a first phase preserving amplifier connected to the first coupler and a second coupler, and the second phase preserving amplifier connected to the first coupler and the second coupler.

Abstract: According to some aspects, a method is provided of operating a circuit quantum electrodynamics system that includes a physical qubit dispersively coupled to a quantum mechanical oscillator, the method comprising applying a first electromagnetic pulse to the physical qubit based on a number state of the quantum mechanical oscillator, wherein the first electromagnetic pulse causes a change in state of the quantum mechanical oscillator, and applying, subsequent to application of the first electromagnetic pulse, a second electromagnetic pulse to the quantum mechanical oscillator that coherently adds or removes energy from the quantum mechanical oscillator.

Abstract: According to some aspects, a quantum mechanical system is provided, comprising a resonator having a plurality of superconducting surfaces and configured to support at least one electromagnetic oscillation mode within a three-dimensional region, wherein the plurality of superconducting surfaces include a first superconducting surface that defines a first plane, and a physical qubit comprising at least one planar component that is planar within the first plane and borders the three-dimensional region.

Abstract: According to some aspects, a circuit is provided comprising a plurality of Josephson junctions arranged in series in a loop, at least one magnetic element producing magnetic flux through the loop, a plurality of superconducting resonators, each resonator coupled to the loop between a different neighboring pair of Josephson junctions of the plurality of Josephson junctions, a plurality of ports, each port coupled to at least one of the plurality of resonators at ends of the resonators opposite to ends at which the resonators are coupled to the loop, and at least one controller configured to provide input energy to each of the plurality of ports that causes the circuit to function as a circulator between the plurality of ports.

Abstract: Some embodiments are directed to a device including multiple substrates comprising one or more troughs. The substrates are disposed such that the one or more troughs form at least one enclosure. At least one superconducting layer covers at least a portion of the at least one enclosure. Other embodiments are directed to a method for manufacturing a superconducting device. The method includes acts of forming at least one trough in at least a first substrate; covering at least a portion of the first substrate with a superconducting material; covering at least a portion of a second substrate with the superconducting material; and bonding the first substrate and the second substrate to form at least one enclosure comprising the at least one trough and the superconducting material.

Abstract: Some embodiments are directed to a device including multiple substrates comprising one or more troughs. The substrates are disposed such that the one or more troughs form at least one enclosure. At least one superconducting layer covers at least a portion of the at least one enclosure. Other embodiments are directed to a method for manufacturing a superconducting device. The method includes acts of forming at least one trough in at least a first substrate; covering at least a portion of the first substrate with a superconducting material; covering at least a portion of a second substrate with the superconducting material; and bonding the first substrate and the second substrate to form at least one enclosure comprising the at least one trough and the superconducting material.