Classifications

• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06N—COMPUTING ARRANGEMENTS BASED ON SPECIFIC COMPUTATIONAL MODELS
  • G06N10/00—Quantum computing, i.e. information processing based on quantum-mechanical phenomena
  • G06N10/40—Physical realisations or architectures of quantum processors or components for manipulating qubits, e.g. qubit coupling or qubit control
• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06N—COMPUTING ARRANGEMENTS BASED ON SPECIFIC COMPUTATIONAL MODELS
  • G06N10/00—Quantum computing, i.e. information processing based on quantum-mechanical phenomena
  • G06N10/60—Quantum algorithms, e.g. based on quantum optimisation, quantum Fourier or Hadamard transforms
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
  • H04B10/70—Photonic quantum communication
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L63/00—Network architectures or network communication protocols for network security
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
  • H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
  • H04L9/0816—Key establishment, i.e. cryptographic processes or cryptographic protocols whereby a shared secret becomes available to two or more parties, for subsequent use
  • H04L9/0852—Quantum cryptography

Definitions

• the present invention relates in general to semiconductor processing and computer processors.
• the present invention relates to a distributed microwave quantum computing system.
• a quantum node includes one or more communication qubits, one or more interior qubits coupled to the one or more communication qubits with interior tunable couplers, a communication tunable coupler coupled to each of the one or more communication qubits, and a communication resonator coupled to each of the communication tunable couplers.
• the one or more interior qubits comprise a set of series connected qubits, a set of parallel connected qubits, or an array of interconnected qubits.
• a readout resonator is coupled to each of the one or more communication qubits and the one or more interior qubits.
• the readout resonator is used for projective measurement to implement heralding-based entanglement.
• a control connector is coupled to each of the interior tunable couplers and the communication tunable couplers.
• an alternating current or radio frequency (AC/RF) signal is applied to the interior tunable coupler or the communication tunable coupler via the control connector to cause parametric photon swap.
• AC/RF alternating current or radio frequency
• a controller is coupled to the control connector, wherein the controller generates the AC/RF signal.
• a drive connector coupled to each of the one or more communication qubits and the one or more interior qubits.
• the communication resonator allows definition of a communication channel for high efficiency photon exchange between the quantum node and other quantum nodes.
• the communication resonator enhances a parametric photon release rate via resonance enhancement and modification to an electromagnetic density of states of the communication channel.
• the one or more communication qubits simultaneously release into a frequency band in the communication channel.
• the communication resonator limits noise from propagating into the quantum node from a coaxial cable or coplanar waveguide.
• an effective loss of photon transfer into or out of the quantum node is reduced using a dark mode.
• the communication resonator rejects an unwanted parametric sideband.
• the quantum node does not require any radio-frequency single-photon-detector nodes or radio-frequency beam-splitters.
• a distributed quantum computing system includes two or more quantum nodes, wherein each quantum node includes one or more communication qubits, one or more interior qubits coupled to the one or more communication qubits with interior tunable couplers, a communication tunable coupler coupled to each of the one or more communication qubits, and a communication resonator coupled to each of the communication tunable couplers.
• One or more coaxial cables or coplanar waveguides connect the two or more quantum nodes together using at least one of the communication resonators of the two or more quantum nodes.
• the two or more quantum nodes are different or substantially identical to one another.
• the two or more quantum nodes are superconducting quantum nodes.
• the one or more interior qubits comprise a set of series connected qubits, a set of parallel connected qubits, or an array of interconnected qubits.
• a readout resonator is coupled to each of the one or more communication qubits and the one or more interior qubits.
• the readout resonator is used for projective measurement to implement heralding -based entanglement.
• a control connector is coupled to each of the interior tunable couplers and the communication tunable couplers.
• an AC/RF signal is applied to the interior tunable coupler or the communication tunable coupler via the control connector to cause parametric photon swap.
• a controller is coupled to the control connector, wherein the controller generates the AC/RF signal.
• a drive connector is coupled to each of the one or more communication qubits and the one or more interior qubits.
• the communication resonator allows definition of a communication channel for high efficiency photon exchange between the quantum node and other quantum nodes.
• the communication resonator enhances a parametric photon release rate via resonance enhancement and modification to an electromagnetic density of states of the communication channel.
• the one or more communication qubits simultaneously release into a frequency band in the communication channel.
• the communication resonator limits noise from propagating into the two or more quantum nodes from the coaxial cable or coplanar waveguide. In another aspect, an effective loss of photon transfer into or out of the two or more quantum nodes is reduced using a dark mode. In another aspect, the communication resonator rejects an unwanted parametric sideband. In another aspect, the system does not require any radio-frequency single-photon-detector nodes or radio-frequency beam-splitters. In another aspect, the system is scalable.
• a method of fabricating a quantum node includes depositing a first metal on a top of a substrate, coating the first metal with a first photoresist, selectively removing the first photoresist to leave a first pattern, etching the first metal to transfer the first pattern to the first metal to form a ground plane that will contain one or more communication qubits, one or more interior qubits, one or more interior tunable couplers, one or more communication tunable couplers, one or more communication resonators, and control lines, removing the first photoresist, depositing a second metal in a second pattern, oxidizing an outer portion of the second metal, and depositing a third metal in a third pattern.
• the combination of the first metal, the second metal, the oxidized outer portion of the second metal and the third metal form the one or more communication qubits, the one or more interior qubits coupled to the one or more communication qubits with the one or more interior tunable couplers, and the communication tunable coupler coupled to each of the one or more communication qubits and each of the one or more communication resonators.
• the first metal comprises aluminum, niobium or tantalum, and the second and third metal comprise aluminum.
• the method further includes fabricating a wiring wafer containing control lines and co-planar waves, and bonding the wiring wafer to the quantum node.
• the method further includes bonding the wiring wafer to a printed circuit board.
• a loss-resistant entanglement protocol for three or more quantum nodes includes: (a) providing the three or more quantum nodes comprising a first quantum node connected to a second quantum node with a first coaxial cable or a first coplanar waveguide, the second quantum node connected to a third quantum node with a second coaxial cable or a second coplanar waveguide, and wherein each of the first quantum node, the second quantum node and the third quantum node comprise: a first qubit, a second qubit, a third qubit, a first interior tunable coupler connected between the first qubit and the second qubit, a second interior tunable coupler connected between the second qubit and the third qubit, a first communication tunable coupler connected to the first qubit, a second communication tunable coupler connected to the third qubit, a first communication resonator coupled to the first communication tunable coupler, and a second communication resonator coupled to the second communication
• (f) further comprises repeating (b), (c), (d) and (e) until the third qubit of the first quantum node and the third qubit of the second quantum node were measured to be in the 1 state in (e).
• (j) further comprises repeating (b), (c), (d), (e), (f), (g), (h) and (i) until the third qubit of the first quantum node and the third qubit of the second quantum node were measured to be in the 1 state in (e) and (i).
• a loss-resistant entanglement protocol for two quantum nodes includes: (a) providing the two quantum nodes comprising a first quantum node connected to a second quantum node with a coaxial cable or a coplanar waveguide, and wherein each of the first quantum node and the second quantum node comprise: a first qubit, a second qubit, a third qubit, a first interior tunable coupler connected between the first qubit and the second qubit, a second interior tunable coupler connected between the second qubit and the third qubit, a first communication tunable coupler connected to the first qubit, a second communication tunable coupler connected to the third qubit, a first communication resonator coupled to the first communication tunable coupler, and a second communication resonator coupled to the second communication tunable coupler; (b) setting the third qubit of the first quantum node and a communication channel mode to a 0 state, and the second qubit of the first quantum
• (f) further comprises repeating (b), (c), (d) and (e) until the third qubit of the first quantum node was measured to be in the 1 state in (e).
• (j) further comprises repeating (b), (c), (d), (e), (f), (g), (h) and (i) until the third qubit of the first quantum node was measured to be in the 1 state in (e) and (i).
• FIGURE 1 is a block diagram of a quantum node in accordance with one embodiment of the present disclosure
• FIGURES 2A-2C are block diagrams showing one or more interior qubits arrainged together in various non-limiting strutures in accordance with one embodiment of the present disclosure
• FIGURE 3 depicts a device mask and microscopic image for a three-qubit quantum node in accordance with one embodiment of the present disclosure
• FIGURE 4 depicts a loss-resistant entanglement protocol between Node-1 and Node-3 in accordance with one embodiment of the present disclosure
• FIGURES 5A-5C are flow charts of the loss-resistant entanglement protocol between Node-1 and Node-3 in accordance with one embodiment of the present disclosure
• FIGURE 6A is a protocol chart of a loss-resistant entanglement protocol between Node-1 and Node-2 in accordance with one embodiment of the present disclosure
• FIGURE 6B is a plot of the click probability and entaglement fidelity for the loss-resistant entanglement protocol between Node-1 and Node-2 in accordance with one embodiment of the present disclosure.
• FIGURE 6C is a plot of the qubit decoherence limited fidelity for the loss-resistant entanglement protocol between Node-1 and Node-2 in accordance with one embodiment of the present disclosure.
• FIGURES 7A-7B are flow charts of the loss-resistant entanglement protocol between Node-1 and Node-2 in accordance with one embodiment of the present disclosure
• FIGURE 8 depicts a parametric photon exchange (SWAP) between a communication qubit of the quantum node and the communication resonators of two quantum nodes and the coaxial cable/coplanar waveguide in accordance with one embodiment of the present disclosure.
• SWAP parametric photon exchange
• FIGURE 9 depicts a method of fabricating a quantum node in accordance with one embodiment of the present disclosure
• FIGURE 10 depicts a fabrication process in accordance with one embodiment of the present disclosure.
• FIGURES 11A-11C depict a method of fabricating a flip-chip quantum cluster on wafer in accordance with one embodiment of the present disclosure.
• testbed for multi-node entanglement network protocols. Users can see the performance of their error resistant protocols in action on real quantum hardware in the near-term.
• the testbed is supposed to be versatile meaning that it is easily reconfigurable and scalable per the needs of users in a co-design way by combining the scalability of superconducting quantum processors and the extensibility of entanglement network. This should provide a unique opportunity for the distributed quantum information processing community.
• quantum devices can have incompatible fabrication processes and even incompatible operation environment.
• incompatible devices can often offer unique capabilities that are not accessible using compatible technologies.
• quantum microwave-optical transducers require processes that involve materials relatively lossy in microwave and operate with strong optical input that is detrimental to superconducting qubit coherence.
• such transducers provide the capability to entangle microwave quantum computing devices over a large distance via optical fiber, making the quantum internet with powerful superconducting quantum computers possible in the future.
• Local quantum entanglement network can allow high-fidelity transfer of quantum state between incompatible devices and incorporation of such transducers as quantum network cards to superconducting quantum computers.
• photon release filter (“communication resonator”) allows definition of communication channel for high efficiency photon exchange between quantum nodes.
• This photon release filter (1) limits the noise propagating into the high-coherence nodes from the lossy RF cable connecting quantum nodes; (2) enhances the parametric photon release rate via resonance enhancement and modification to electromagnetic density of states of the communication channel; and (3) rejects the unwanted parametric sideband since the qubit can simultaneously release into two frequency bands if the channel has no photon release fdter to define one communication band. This restriction significantly increases the photon release fidelity.
• the methods use heralding for loss-resistant entanglement generation between nodes connected via lossy RF cables or coplanar waveguides.
• the heralding protocol is designed and implemented completely within quantum processing units (quantum nodes) without using separate RF single-photon-detector nodes and lossy RF beam-splitters. This simplification and innovation make the efficiency of entanglement generation higher by more than one order of magnitude and removed the stringent constraints in fabricating parameter matched narrow-band quantum processor nodes and single-photon-detector detector nodes.
• the method is the only method combining the scalability of 2D (planar) quantum processor architecture (References 1 and 4) with heralding based loss-resistant microwave entanglement generation (Reference 3).
• This architecture is the unavoidable enabler technology to enable the scaling of superconducting quantum computing technologies beyond the near-term stage into large-scale quantum computing cluster that can produce critical quantum computational power to solve and accelerate solving challenging computational tasks in designing new drugs, new materials, new chemicals, and cutting-edge quantum-enabled artificial intelligence which will significantly alter the future of computation industry as well as industries relying on it.
• This technology can be used to build cutting-edge industry leading quantum computers for disrupting the computing industry for many years.
• Various embodiments described herein have numerous advantages, which may include, but are not limited to: (l)“Mature” and scalable technology for advanced quantum logics; (2) Based on established micro/nano-fabrication infrastructure for rapid fabrication and testing; (3) Straightforward and efficient programmable qubit-photon parametric transduction tailored to various protocols’ requirements; and/or (4) Accessible (cloud) protocol testbed for users and direct application in distributed microwave quantum computing.
• Some embodiments may be limited to cryogenic space and interconnect with fiber-optical network using a quantum optic-microwave transducer.
• the quantum node 100 includes two or more communication qubits 102, 106, one or more interior qubits 104 coupled between the two or more communication qubits 102, 106 with interior tunable couplers 108, a communication tunable coupler 110 coupled to each of the one or more communication qubits 102, 106, and a communication resonator 112 coupled to each of the communication tunable couplers 110.
• the two or more communication qubits 102, 106 and one or more interior qubits 104 can be, but are not required to be, identical to one another.
• interior tunable couplers 108 and the communication tunable couplers 110 can be, but are not required to be, identical to one another.
• the names merely denote the placement of the components within the quantum node.
• the one or more interior qubits 104 can be arrainged together in any desired struture such as, but not limited to, a set of series connected qubits (FIGURE 2A), a set of parallel connected qubits (FIGURE 2B), an array of interconnected qubits (FIGURE 2C), etc.
• any of the interior qubits 104 may be connected to a communication tunable coupler 110, which is connected to a communication resonator 112. In such a case, the interior qubit 104 essentially becomes a communication qubit 102, 106.
• the quantum node 100 is configurable and scalable to satisfy any desired operating characteristics.
• the quantum node includes one or more communication qubits and one or more interior qubits 104 coupled to the one or more communication qubits.
• a readout resonator 114 is coupled to each of the one or more communication qubits 102, 106 and the one or more interior qubits 104.
• the readout resonator 114 may be used for projective measurement to implement heralding-based entanglement.
• a control connector 116 is coupled to each of the interior tunable couplers 108 and the communication tunable couplers 110.
• An alternating current or radio frequency (AC/RF) signal can be applied to the interior tunable coupler 108 or the communication tunable coupler 110 via the control connector 116 to cause parametric photon swap.
• a controller 118 can be coupled to the control connectors 116, wherein the controller 118 can operate at room temperature and generates the AC/RF signal.
• a drive connector 120 is coupled to each of the one or more communication qubits 102, 106 and the one or more interior qubits 104. Note that the drive connection 120 applies single-qubit operations on each qubit. For example, changing the stage of the qubit from 0 -> l or l -> 0 or 0 -> a superposition state like (
• the communication resonators 112 (coupled with coaxial cable or coplanar waveguide modes) allow definition of a communication channel for high efficiency photon exchange between the quantum node 100 and other quantum nodes (not shown). Moreover, the communication resonators 112 enhance a parametric photon release rate via resonance enhancement and modification to an electromagnetic density of states of the communication channel. The two or more communication qubits 102, 106 and the one or more interior qubits 104 can simultaneously release into a frequency band in the communication channel. Moreover, the communication resonators 112 can limit noise from propagating into the quantum node 100 from a coaxial cable, coplanar waveguide or other type of suitable connector or waveguide (not shown) connected to the communication resonators 112.
• An effective loss of photon transfer into or out of the quantum node 100 can be reduced using a dark mode.
• a dark mode is a resonance or communication mode formed by the hybridization of two communication resonators and the coaxial-cable/coplanar waveguide or other connector/waveguide coupled to both of them. It is “dark” because it has minimal energy participation in the lossy coaxial-cable/coplanar waveguide region.
• the communication resonators 112 can also reject an unwanted parametric sideband during photon swap between a qubit and a communication resonator.
• the quantum node 100 does not require any radio-frequency single-photon-detector nodes or radio-frequency beam-splitters.
• FIGURES 2A-2C block diagrams showing one or more interior qubits 104 arrainged together in various non-limiting strutures in accordance with one embodiment of the present disclosure are shown.
• FIGURE 2A depicts a set of series connected qubits 104a, 104b, ... , 104n.
• FIGURE 2B depicts a set of parallel connected qubits 104a, 104b, 104c, ... , 104n and 104d, 104e, 104f ... , 104m.
• FIGURE 2C depicts an array of interconnected qubits 104n, 104I 2 , 104I 3 , ... , 104 in and 104 21 , 104 22 , 104 23 ... , 104 in and 104 ib 104 i2 , 104 i3 ... , 104 in .
• FIGURE 3 a device mask 300 and microscopic image 302 for a three-qubit quantum node, such as quantum node 100 in (FIGURE 1) in accordance with one embodiment of the present disclosure are shown.
• the quantum node includes three qubits 304, 306, 308 that are coupled together in series with tunable couplers 310.
• a communication resonator 312 is coupled to each of the tunable couplers 310 that are connected to the exterior qubits 304, 308.
• the qubits 304, 306, 308 are identical to one another.
• the tunable couplers 310 are identical to one another.
• a readout resonator (Qubit-Readout) 314 is coupled to each of the qubits 304, 306, 308 and is used to carry out projective measurement for implementing the heralding-based loss-resistant quantum entanglement generation as described below.
• a control connector (Coupler-Z) 316 is coupled to each of the tunable couplers 310 and is used to contol the tunable couplers 310 between the qubits for two-qubit gate or between qubits and the communication resonators for parametric photon release or capture.
• a drive connector (XY-Drive) 318 is coupled to each of the qubits 304, 306, 308 and is used for carry out single qubit gate on the connected transmon qubit.
• FIGURE 4 a loss-resistant entanglement protocol between Node-1 and Node-3 in accordance with one embodiment of the present disclosure is shown.
• This illustration only focuses on loss-resistant heralding-based entanglement generation and high-fidelity entanglement swap in a linear quantum network of three quatum nodes Node-1, Node-2, Node-3.
• the three superconducting quantum nodes Node-1, Node-2, Node-3 are substantially identical, and each contains three transmon qubits Qy wherein i represents the node number and J representes the qubit number. Note that the quantum nodes can be different from one another in other embodiments.
• the three quantum nodes Node- 1, Node-2, Node-3 are connected to each other via coaxial cables 402 (illustrated as the red cylinder).
• the coaxial cables 402 are represented by Ty wherein the transmisson line mode connectes Node-z and Node- Coplanar waveguides can be used instead of the coaxial cables 402.
• the three qubits in each node are indicated with the light-blue letter Q, and there are also four tunable couplers 404 that are used to generated two-qubit gates on-demand. There is also the on- chip coupling to the coaxial transmission line 402 (also referred to as coaxial cable) via the communication resonators 406.
• the qubit readout resonators are used for projective measurements that are needed for implementing the heralding-based entanglement generation.
• This example is called a baseline because it is designed to demonstrate the basic functionalities needed to build scalable entanglement network with advanced quantum nodes and encoding.
• More complicated quantum processor nodes can be engineered by adding more transmon qubits since only three qubit each nodes are needed for generate entanglement via lossy cables with heralding. More nodes can be added since the entanglement generation and swap can be concatenated together to create a large multi-node entanglement network.
• the three or more quantium nodes include a first quantum node connected to a second quantum node with a first coaxial cable or a first coplanar waveguide, the second quantum node connected to a third quantum node with a second coaxial cable or a second coplanar waveguide, and wherein each of the first quantum node, the second quantum node and the third quantum node comprise: a first qubit, a second qubit, a third qubit, a first interior tunable coupler connected between the first qubit and the second qubit, a second interior tunable coupler connected between the second qubit and the third qubit, a first communication tunable coupler connected to the first qubit, a second communication tunable coupler connected to the third qubit, a first communication resonator coupled to the first communication tunable coupler, and a second communication resonator coupled to the second communication tunable coupler.
• coaxial cables or coplanar waveguides can also refer to other types of suitable connectors or waveguides.
• the third qubit of the first quantum node, a first communication channel mode (formed by the hybridization of the second communication resonator of the first quantum node, first communication resonator of the second quantum node, and the first coaxial cable or the first coplanar waveguide), the third qubit of the second quantum node and a second communication channel mode (formed by the hybridization of the second communication resonator of the second quantum node, first communication resonator of the third quantum node, and the second coaxial cable or the second coplanar waveguide) are set to a 0 state, and the second qubit of the first quantum node, the first qubit of the second quantum node, the second qubit of the second quantum node and the first qubit of the third quantum node are set to a 1 state.
• half-way of a two qubit swap is performed between: (1) the second qubit of the first quantum node and the third qubit of the first quantum node (2) the first coaxial cable or the first coplanar waveguide and the first qubit of the second quantum node, (3) the second qubit of the second quantum node, and (4) the second coaxial cable or the second coplanar waveguide and the first qubit of the third quantum node.
• half-way of the two qubit swap is performed between: (1) the third qubit of the first quantum node and the first coaxial cable or the first coplanar waveguide, and (2) the third qubit of the second quantum node and the second coaxial cable or the second coplanar waveguide or.
• the third qubit of the first quantum node and the third qubit of the second quantum node are measured.
• the third qubit of the first quantum node and the first communication channel mode (formed by the hybridization of the second communication resonator of the first quantum node, first communication resonator of the second quantum node, and the first coaxial cable or the first coplanar waveguide) are set to the 0 state if the third qubit of the first quantum node was measured to be in the 1 state at 510, and the third qubit of the second quantum node and the second communication channel mode (formed by the hybridization of the second communication resonator of the second quantum node, first communication resonator of the third quantum node, and the second coaxial cable or the second coplanar waveguide) are set to the 0 state if the third qubit of the second quantum node was measured to be in the 1 state at 510.
• flipping (1) a state of the third qubit of the first quantum node if the second qubit of the first quantum node is in the 1 state, (2) a state of the first coaxial cable or the first coplanar waveguide if the first qubit of the second quantum node is in the 1 state, (3) a state of the third qubit of the second quantum node if the second qubit of the second quantum node is in the 1 state, and (4) a state of the second coaxial cable or the second coplanar waveguide if the first qubit of the third quantum node is in the 1 state.
• half-way of the two qubit swap is performed between: (1) the third qubit of the first quantum node and the first coaxial cable or the first coplanar waveguide, and (2) the third qubit of the second quantum node and the second coaxial cable or the second coplanar waveguide.
• the third qubit of the first quantum node and the third qubit of the second quantum node are measured.
• a first entanglement is established between the second qubit of the first quantum node and the first qubit of the second quantum node if the third qubit of the first quantum node was measured to be the 1 state in 510 and 518
• a second entanglement is established between the second qubit of the second quantum node and the first qubit of the third quantum node if the third qubit of the second quantum node is measured to be the 1 state in 510 and 518.
• a third entanglement is established between the second qubit of the first quantum node and the first qubit of the third quantum node.
• the quantum entanglement needs both 510 and 518 to measure the third qubit of the first quantum node and the third qubit of the second quantum node in the 1 state.
• the protocol could be re-run from 504 until 510 produces the 1 state measurements after which the protocol can continue to reset relevant states in 512.
• the protocol could be re-run from 504 until 510 and 518 produce the 1 state measurements after which the first and second entaglements are established in 520.
• step 512 further comprises repeating steps 502, 504, 506 and 508 until the third qubit of the first quantum node was measured to be in the 1 state in step 510.
• step 518 further comprises repeating 502, 504, 506, 508, 510, 512, 514 and 516 until the third qubit of the first quantum node was measured to be in the 1 state in steps 512 and 518.
• the protocol could be run from 504 to 524 multiple rounds without real-time feedforward controls and post-select results of rounds where 510 and 518 produce the 1 state measurements after which the first and second entaglements are established in 520. Note that this sequence is less efficient than the sequences with real-time feedforward controls described in the previous paragraph.
• the two quantium nodes include a first quantum node connected to a second quantum node with a coaxial cable or a coplanar waveguide, and wherein each of the first quantum node and the second quantum node comprise: a first qubit, a second qubit, a third qubit, a first interior tunable coupler connected between the first qubit and the second qubit, a second interior tunable coupler connected between the second qubit and the third qubit, a first communication tunable coupler connected to the first qubit, a second communication tunable coupler connected to the third qubit, a first communication resonator coupled to the first communication tunable coupler, and a second communication resonator coupled to the second communication tunable coupler.
• coaxial cables or coplanar waveguides can also refer to other types of suitable connectors or waveguides.
• the third qubit of the first quantum node and a communication channel mode (formed by hybridization of the second communication resonator of the first quantum node, the first communication resonator of the second quantum node, and the coaxial cable or the coplanar waveguide) are set to a 0 state, and the second qubit of the first quantum node and the first qubit of the second quantum node are set to a 1 state.
• half-way of a two qubit swap is performed between: (1) the second qubit of the first quantum node and the third qubit of the first quantum node, and (2) the coaxial cable or the coplanar waveguide and the first qubit of the second quantum node.
• the third qubit of the first quantum node is measured.
• the third qubit of the first quantum node and the communication channel mode (formed by hybridization of the second communication resonator of the first quantum node, the first communication resonator of the second quantum node, and the coaxial cable or the coplanar waveguide) are set to the 0 state if the third qubit of the first quantum node was measured to be in the 1 state in 710.
• flipping (1) a state of the third qubit of the first quantum node if the second qubit of the first quantum node is in the 1 state, and (2) a state of the coaxial cable or the coplanar waveguide if the first qubit of the second quantum node is in the 1 state.
• CNOT quantum controlled-NOT gates
• the quantum nature of the gate means it happens as a natural observation-free intrinsic quantum process.
• an entanglement is established between the second qubit of the first quantum node and the first qubit of the second quantum node if the third qubit of the first quantum node was measured to be in the 1 state in 710 and 718.
• step 712 further comprises repeating steps 702, 704, 706 and 708 until the third qubit of the first quantum node was measured to be in the 1 state in step 710.
• step 718 further comprises repeating 702, 704, 706, 708, 710, 712, 714 and 716 until the third qubit of the first quantum node was measured to be in the 1 state in steps 712 and 718.
• FIGURE 6B is a plot of the click probability and entaglement fidelity for the loss-resistant entanglement protocol between Node-1 and Node-2 in accordance with one embodiment of the present disclosure.
• success of loss-resistant entanglement protocol step 710 is the First Click 602 (solid black line)
• success of loss-resistant entanglement protocol step 718 is the Second Click 604 (dashed black line).
• Success of the two steps 710 and 718 in one sequence of execution is Double Click 606 (dash-dot black line), which is the flag of a successful sequence from beginning to end to entangle Node-1 and Node-2.
• the First Click Fidelity 608 (solid blue line) and Second Click Fidelity 610 are also shown.
• FIGURE 6C is a plot of the qubit decoherence limited fidelity for the loss-resistant entanglement protocol between Node-1 and Node-2 in accordance with one embodiment of the present disclosure.
• the First Click State 650 solid black line
• Second Click State 655 dashed black line
• FIGURE 8 depicts a photon exchange (SWAP) between a communication qubit of one quantum node and the communication resonators of two quantum nodes Node-1, Node-2 and the coaxial cable/coplanar waveguide 402 in accordance with one embodiment of the present disclosure.
• Q o , Qi and Q 2 are the qubits in quantum nodes Node-1, Node-1.
• Line 802 blue line
• line 804 range line
• line 806 green line
• line 808 red line
• line 810 is the second communication resonator.
• the distributed quantum computing system includes two or more quantum nodes Node-1, ... , Node-N, wherein each quantum node Node-1, ... , Node-N includes one or more communication qubits 102, 106, one or more interior qubits 104 coupled to the one or more communication qubits 102, 106 with interior tunable couplers 108, a communication tunable coupler 110 coupled to each of the one or more communication qubits 102, 106, and a communication resonator 112 coupled to each of the communication tunable couplers 110.
• One or more coaxial cables or coplanar waveguides 402 connect the two or more quantum nodes Node-1, . . . , Node-N together using at least one of the communication resonators 112 of the two or more quantum nodes Node-1, ... , Node-N.
• the two or more quantum nodes Node-1, ... , Node-N can be different or substantially identical to one another.
• the two or more quantum nodes Node-1, ... , Node-N can be superconducting quantum nodes. An effective loss of photon transfer into or out of the two or more quantum nodes Node-1, . . . , Node-N is reduced using a dark mode.
• the system is scalable.
• the one or more communication qubits 102, 106 and one or more interior qubits 104 are identical to one another.
• the interior tunable couplers 108 and the communication tunable couplers 110 are identical to one another.
• the names merely denote the placement of the components within the quantum node.
• the one or more interior qubits 104 can be arrainged together in any desired struture such as, but not limited to, a set of series connected qubits (FIGURE 2A), a set of parallel connected qubits (FIGURE 2B), an array of interconnected qubits (FIGURE 2C), etc.
• any of the interior qubits 104 may be connected to a communication tunable coupler 110, which is connected to a communication resonator 112.
• the quantum node 100 is configurable and scalable to satisfy any desired operating characteristics.
• a readout resonator 114 is coupled to each of the two or more communication qubits 102, 106 and the one or more interior qubits 104.
• the readout resonator 114 may be used for projective measurement to implement heralding-based entanglement.
• a control connector 116 is coupled to each of the interior tunable couplers 108 and the communication tunable couplers 110.
• An AC/RF signal can be applied to the interior tunable coupler 108 or the communication tunable coupler 110 via the control connector 116 to cause parametric photon swap.
• a controller 118 can be coupled to the control connectors 116, wherein the controller 118 can operate at room temperature and generates the AC/RF signal.
• a drive connector 120 is coupled to each of the one or more communication qubits 102, 106 and the one or more interior qubits 104.
• the communication resonators 112 allow definition of a communication channel for high efficiency photon exchange between the quantum node 100 and other quantum nodes (not shown). Moreover, the communication resonators 112 enhance a parametric photon release rate via resonance enhancement and modification to an electromagnetic density of states of the communication channel. The two or more communication qubits 102, 106 and the one or more interior qubits 104 can simultaneously release into a frequency band in the communication channel. Moreover, the communication resonators 112 can limit noise from propagating into the quantum node 100 from a coaxial cable or coplanar waveguide (not shown) connected to the communication resonators 112. An effective loss of photon transfer into or out of the quantum node 100 can be reduced using a dark mode. The communication resonators can also reject an unwanted parametric sideband. Finally, the quantum node 100 does not require any radio-frequency single-photon-detector nodes or radio-frequency beam-splitters.
• a method 900 of fabricating a quantum node in accordance with one embodiment of the present disclosure is shown.
• a first metal is deposited on a top of a substrate in block 902, the first metal is coated with a first photoresist in block 904, and the first photoresist is selectively removed to leave a first pattern in block 906.
• the first metal is etched to transfer the first pattern to the first metal to form a ground plane and one or more communication resonators in block 908, and the first photoresist is removed in block 910.
• a second metal is deposited in a second pattern in block 912, an outer portion of the second metal is oxidized in block 914, and a third metal is deposited in a third pattern in block 916.
• the combination of the first metal, the second metal, the oxidized outer portion of the second metal and the third metal form one or more communication qubits, one or more interior qubits coupled to the one or more communication qubits with interior tunable couplers, and a communication tunable coupler coupled to each of the one or more communication qubits and each of the one or more communication resonators in block 918.
• the first metal can be, but is not limited to aluminum, niobium, tantalum or other superconducting metal.
• the second and third metal can be, but is not limited to aluminum or other superconducting metal.
• Other steps may include: fabricating a wiring wafer containing control lines and co-planar wave, and bonding the wiring wafer to the quantum node; or bonding the wiring wafer to a printed circuit board.
• FIGURE 10 a fabrication process 1000 in accordance with one embodiment of the present disclosure is shown.
• the aluminum can be niobium, tantalum or other super conducting metal.
• Step 1 Initial wafer cleaning of the silicon substrate 1002 (black) : (la) clean with Piranha solution and (lb) clean with dilute HF solution.
• Step 2 Deposit an aluminum ground plane 1004 (orange) on the silicon substrate 1002.
• Step 3 Pattern titanium 1006 (gray) as alignment markers on the ground plane 1004: (3a) resist coating, (3b) electron beam exposures, (3c) develop, (3d) titanium deposition, and (3e) acetone lift off.
• Step 4 Pattern the aluminum ground plane 1004 and resonators: (4a) resist coating, (4b) electron beam exposure, (4c) develop, (4d) aluminum etch to remove unwanted aluminum, and (4) wafter cleaning to remove resist on top.
• the ground plane 1004 will contain one or more communication qubits, one or more interior qubits, one or more interior tunable couplers, one or more communication tunable couplers, one or more communication resonators, and control lines (collectively 1808).
• Step 5 Pattern aluminum, aluminum oxide and aluminum junctions: (5a) resist coating, (5b) electron beam exposure, (5c) develop, (5d) first aluminum deposition 1010 (yellow), aluminum oxidation 1012 (blue) and the second aluminum deposition 1014 (red) with different angle, and (5e) acetone lift off.
• the combination of the first metal, the second metal, the oxidized outer portion of the second metal and the third metal form the one or more communication qubits, the one or more interior qubits coupled to the one or more communication qubits with the one or more interior tunable couplers, and the communication tunable coupler coupled to each of the one or more communication qubits and each of the one or more communication resonators.
• FIGURES 11A-11C a method of fabricating a flip-chip quantum cluster on wafer in accordance with one embodiment of the present disclosure is shown.
• Each quantum node 1102 is bonded to a wiring wafer 1104, which in turn is connected to a PCB board 1106.
• the quantum nodes 1102 are connected together with coplanar waveguides 1108.
• the wiring wafer 1104 contains the necessary control lines and coplanar waveguides forming the communication channel with communication resonators in the quantum nodes.
• the aluminum can be niobium, tantalum or other superconducting metal.
• the wiring wafer 1104 processing steps 1110 are illustrated in FIGURE 11B:
• Step 1 Initial wafer cleaning of the silicon substrate 1112 (black): (la) clean with Piranha solution and (lb) clean with dilute HF solution.
• Step 2 Through silicon via (TSV) definition: (2a) resist coating, (2b) lithography, (2c) develop, (2d) RIE Bosch process for silicon deep etch to create vertical through silicon wafer tunnels 1114, (2e) ALD TiN conformal metalization of the silicon wafer tunnels to form superconduction TSVs (PECVD Al and other suitable materials may also be used), and (2f) chemical-mechanical-polish (CMP) to remove silicon thickness and expose TSVs to surfaces.
• TSV Through silicon via
• Step 3 Define silicon hardspaces: (3a) resist coating, (3b) lithography, (3c) develop, (3d) silicon dry etch to remove most areas 1116 to be metalized with superconducting circuit and remaining unetched area become silicon hard spacer 1108 for defining flip-chip bonding height.
• Step 4 Deposit superconducting metal (Nb) 1110 in area 1116 between the hard spacers 1118.
• Step 5 Pattern titanium as alignment markers 1122 : (5a) resist coating, (5b) lithography, (5c) develop, (5d) titanium deposition, and (5e) acetone lift off.
• Step 6 Pattern ground plane and resonators 1124: (6a) resist coating, (6b) electron beam exposure, (6c) develop, (6d) metal dry etch to removed unwanted metal, and (6e) wafter cleaning to remove resist on top.
• FIGURE 11C The quantum node 1102 processing steps 1130 are illustrated in FIGURE 11C:
• Step 1 Initial wafer cleaning of the silicon substrate 1132 (black): (la) clean with Piranha solution and (lb) clean with dilute HF solution.
• Step 2 Deposit superconducting metal (Nb) 1134 (orange) on the silicon substrate 1132.
• Step 3 Pattern titanium as alignment markers 1136 (gray): (3a) resist coating, (3b) electron beam exposures, (3c) develop, (3d) titanium deposition, and (3e) acetone lift off.
• Step 4 Pattern ground plane and resonators 1138 (orange): (4a) resist coating, (4b) electron beam exposure, (4c) develop, (4d) metal dry etch to remove unwanted metal, and (4) wafer cleaning to remove resist on top.
• Step 5 Pattern aluminum, aluminum oxide and aluminum junctions: (5a) resist coating, (5b) electron beam exposure, (5c) develop, (5d) first aluminum deposition 1140 (yellow), aluminum oxidation 1142 (blue) and the second aluminum deposition 1144 (red) different angle, and (5e) acetone lift off.
• Step 6 Define indium bond bumps 1146 (light gray): (6a) resist coating, (6b) lithography, (6c) develop, (6d) indium evaporation, and (6e) wafer cleaning to remove resist on top.
• Circuits can be implemented with, but are not limited to, single or combinations of discrete electrical and electronic components, integrated circuits, semiconductor devices, analog devices, digital devices, etc. Elements can be coupled together using any type of suitable direct or indirect connection between the elements including, but not limited to, wires, pathways, channels, vias, electromagnetic induction, electrostatic charges, optical links, wireless communication links, etc. [00111] It will be understood that particular embodiments described herein are shown by way of illustration and not as limitations of the invention. The principal features of this invention can be employed in various embodiments without departing from the scope of the invention. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, numerous equivalents to the specific procedures described herein. Such equivalents are considered to be within the scope of this invention and are covered by the claims.
• the words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”) or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.
• compositions and methods comprising or may be replaced with “consisting essentially of’ or “consisting of.”
• the phrase “consisting essentially of’ requires the specified integer(s) or steps as well as those that do not materially affect the character or function of the claimed invention.
• the term “consisting” is used to indicate the presence of the recited integer (e.g., a feature, an element, a characteristic, a property, a method/process step, or a limitation) or group of integers (e.g., feature(s), element(s), characteristic(s), property(ies), method/process(s) steps, or limitation(s)) only.
• A, B, C, or combinations thereof refers to all permutations and combinations of the listed items preceding the term.
• “A, B, C, or combinations thereof’ is intended to include at least one of: A, B, C, AB, AC, BC, or ABC, and if order is important in a particular context, also BA, CA, CB, CBA, BCA, ACB, BAC, or CAB.
• expressly included are combinations that contain repeats of one or more item or term, such as BB, AAA, AB, BBC, AAABCCCC, CBBAAA, CABABB, and so forth.
• the skilled artisan will understand that typically there is no limit on the number of items or terms in any combination, unless otherwise apparent from the context.
• words of approximation such as, without limitation, “about,” “substantial” or “substantially” refers to a condition that when so modified is understood to not necessarily be absolute or perfect but would be considered close enough to those of ordinary skill in the art to warrant designating the condition as being present. The extent to which the description may vary will depend on how great a change can be instituted and still have one of ordinary skill in the art recognize the modified feature as still having the required characteristics and capabilities of the unmodified feature. In general, but subject to the preceding discussion, a numerical value herein that is modified by a word of approximation such as “about” may vary from the stated value by at least ⁇ 1, 2, 3, 4, 5, 6, 7, 10, 12 or 15%.

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