A computing system includes a quantum processor with qubits, a classical memory including a quantum program defining a plurality of instructions in a source language, and a classical processor configured to: (i) receive a circuit of gates representing a quantum program for a variational algorithm in which computation is interleaved with compilation; (ii) identify a plurality of blocks, each block includes a subcircuit of gates, leaving one or more remainder subcircuits of the circuit of gates outside of the plurality of blocks; (iii) pre-compile each block of the plurality of blocks with a pulse generation program to generate a plurality of pre-compiled blocks including control pulses configured to perform the associated block on the quantum processor; and (iv) iteratively execute the quantum program using the pre-compiled blocks as static during runtime and recompiling the one or more remainder subcircuits on the classical processor at each iteration of execution.
A computing system includes a quantum processor with qubits, a classical memory including a quantum program defining a plurality of instructions in a source language, and a classical processor configured to: (i) receive a circuit of gates representing a quantum program for a variational algorithm in which computation is interleaved with compilation; (ii) identify a plurality of blocks, each block includes a subcircuit of gates, leaving one or more remainder subcircuits of the circuit of gates outside of the plurality of blocks; (iii) pre-compile each block of the plurality of blocks with a pulse generation program to generate a plurality of pre-compiled blocks including control pulses configured to perform the associated block on the quantum processor; and (iv) iteratively execute the quantum program using the pre-compiled blocks as static during runtime and recompiling the one or more remainder subcircuits on the classical processor at each iteration of execution.
A quantum computing system includes a quantum processor having a plurality of qubits, a classical memory, and a classical processor. The classical processor is configured to compile a quantum program into logical assembly instructions in an intermediate language, aggregate the logical assembly instructions together into a plurality of logical blocks of instructions, generate a logical schedule for the quantum program based on commutativity between the plurality of logical blocks, generate a tentative physical schedule based on the logical schedule, the tentative physical schedule includes a mapping of the logical assembly instructions in the logical schedule onto the plurality of qubits of the quantum processor, aggregate instructions together within the tentative physical schedule that do not reduce parallelism, thereby generating an updated physical schedule; generate optimized control pulses for the aggregated instructions, and execute the quantum program on the quantum processor with the optimized control pulses and the updated physical schedule.
A quantum computing system includes a quantum processor having a plurality of qubits, a classical memory, and a classical processor. The classical processor is configured to compile a quantum program into logical assembly instructions in an intermediate language, aggregate the logical assembly instructions together into a plurality of logical blocks of instructions, generate a logical schedule for the quantum program based on commutativity between the plurality of logical blocks, generate a tentative physical schedule based on the logical schedule, the tentative physical schedule includes a mapping of the logical assembly instructions in the logical schedule onto the plurality of qubits of the quantum processor, aggregate instructions together within the tentative physical schedule that do not reduce parallelism, thereby generating an updated physical schedule; generate optimized control pulses for the aggregated instructions, and execute the quantum program on the quantum processor with the optimized control pulses and the updated physical schedule.
A large class of problems in the current era of quantum devices involve interfacing between the quantum and classical system. These include calibration procedures, charac-terization routines, and variational algorithms. The control in these routines iteratively switches between the classical and the quantum computer. This results in the repeated compilation of the program that runs on the quantum system, scaling directly with the number of circuits and iterations. The repeated compilation results in a significant overhead throughout the routine. In practice, the total runtime of the program (classical compilation plus quantum execution) has an additional cost proportional to the circuit count. At practical scales, this can dominate the round-trip CPU-QPU time, between 5% and 80%, depending on the proportion of quantum execution time. To avoid repeated device-level compilation, we identify that machine code can be parametrized corresponding to pulse/gate parameters which can be dynamically adjusted during execution. Therefore, we develop a device-level partial-compilation (DLPC) technique that reduces compilation overhead to nearly constant, by using cheap remote procedure calls (RPC) from the QPU control software to the CPU. We then demonstrate the performance speedup of this on optimal pulse calibration, system characterization using randomized benchmarking (RB), and variational algorithms. We execute this modified pipeline on real trapped-ion quantum computers and observe significant reductions in compilation time, as much as 2.7x speedup for small-scale VQE problems.
A method of determining a pattern in a sequence of bits using a quantum computing system includes setting a first register of a quantum processor in a superposition of a plurality of string index states, encoding a bit string in a second register of the quantum processor, encoding a bit pattern in a third register of the quantum processor, circularly shifting qubits of the second register conditioned on the first register, amplifying an amplitude of a state combined with the first register in which the circularly shifted qubits of the second register matches qubits of the third register, measuring an amplitude of the first register and determining a string index state of the plurality of string index states associated with the amplified state, and outputting, by use of a classical computer, a string index associated with the first register in the measured state.
An apparatus for performing quantum computing includes multiple qubits, each of at least a subset of the qubits comprising a loop formed of a Dirac or Weyl semimetal and having at least two stable quantum states. The apparatus further includes at least one terahertz cavity coupled with the qubits, the terahertz cavity being configured to detect the quantum states of the qubits. Each of at least the subset of qubits is configured to receive a circularly polarized radiation source. The radiation source is adapted to excite a chiral current in each of at least the subset of qubits, the quantum states of the plurality of qubits being a function of the chiral current.
Hybrid quantum-classical computing systems consist of a classical control system that sends quantum circuits and receives measurement results from a quantum co-processor. Such systems allow us to model algorithms that require the classical control system to generate quantum circuits on the fly, potentially based on prior measurement results. This is challenging, as the classical control system must generate quantum circuits that manipulate live quantum states. In this setting, the classical control system is generating further quantum circuits while the quantum co-processor is internally maintaining the state of the live qubits; this is not ideal, since this not only is costly but also introduces additional sources of noise to the live qubits. Thus, we want to minimize the latency between receiving measurement results and sending the next quantum circuit to be executed by pre-computing quantum circuits. We introduce HyQ (pronounced haiku), a multi-modal language based on adjoint logic that pre-generates quantum circuits before executing a hybrid quantum-classical program. We achieve this by separating our semantics into two distinct stages: 1) compile-time generation of quantum circuits and classical runtime code and 2) execution of the classical runtime code that instruments the quantum co-processor. This separation between stages allows us to formally guarantee that all circuit-generation logic occurs before the instrumentation logic, i.e., the actual runtime, and minimizes the idling of the quantum co-processor at runtime. We give a type system, a circuit-normalization semantics for the compile-time stage, which eagerly performs all circuit-generation logic, and a runtime semantics for HyQ that corresponds to the second stage. We prove type preservation and progress for both semantics.