H IMPROVED QUANTUM CIRCUITS PRANAV GOKHALE CASEY DUCKERING S Z VIA DIRTY QUTRITS JONATHAN BAKER FREDERIC CHONG X
CIRCUITS ABSTRACT SIMULATION Circuits represent quantum programs as a +1 (Incrementer) Current efforts towards scaling quantum computer “timeline” of gates. All circuits have been verified. Increment the input qubits (mod 2N) We simulated across a range of realistic error rates for focus on increasing # of qubits or reducing noise. We near-term superconducting and trapped ion systems. propose an alternative strategy: = control on |1⟩ = control on |2⟩ Our SC parameters are based ��� = control on 2 . If k = 1, also control on 0 ��� on current IBM hardware as � ��� � +1 I = |I + 1 JKL 3⟩ FLIP Q/S = |S/Q⟩ well as experimentally- ��� C,. � motivated projections. -� -� � � -��� -��� Multi-Control -��� Our Trapped Ion model Qutrits Apply U to target iff all control bits are 1 Quantum systems have natural access is based on dressed to an infinite spectrum of discrete qutrit experiments. statesàin fact, two-level qubits Our strategy replaces ancilla bits with require suppressing higher states. The qutrits. This enables operation at the underlying physics of qutrits are ancilla-free frontier, where each We simulated the 13-control Toffoli gate over all error similar as those for qubits. hardware qubit is a data qubit. models, using 20,000 CPU hours of simulation time— sufficient to estimate mean fidelities with 2! < 0.1%. All In prior work, qutrits conferred only a lg(3) constant error models achieve >2x better fidelity for our qutrit factor advantage via binary to ternary compression [1- design and as high as 10,000x for current error rates. 4]. We introduce a new technique that maintains binary Due to the asymptotic depth reduction, larger circuits input and output, but uses intermediate qutrit states will attain arbitrarily large fidelity advantages. that replace ancillas. We show that this technique leads +k (Constant Adder) to asymptotically better circuit depths. Our circuit Increment the input qubits by k (mod 2N) constructions have polylog depth, compared to linear depth for qubit-only circuits. We explore the tradeoff of operating higher-error qutrits by performing simulation under realistic noise models. Our simulations suggest that our techniques would significantly improve circuit fidelity by orders of magnitude, even for current device errors and sizes. Our circuit constructions are applicable to a broad range of quantum algorithms, including Grover Search Other Applications and Shor’s Factoring [5, 6]. FUTURE WORK • Grover search (diffusion operator) • Shor’s algorithm (modular exponentiation) The primary conclusion of our work is that qutrit states • Quantum artificial neurons (multi-control Z) are valuable computational resources. These resources BACKGROUND • Logical qubit encoding for error correction have been traditionally overlooked, but this work demonstrates that they can be used to achieve asymptotically better circuit depths. A critical operation for quantum computing is QUTRIT ERROR MODELING Our ongoing work includes: the multiple-controlled - a reversible circuit synthesis tool that automatically Toffoli, which applies an applies dirty qutrit circuit constructions flip gate to a target iff all We modeled depolarizing gate errors and amplitude damping idle errors for both superconducting and trapped ion systems. - an asymptotically improved qutrit circuit for +k Depolarizing [12] Amplitude Damping [13] controls are 1 We also see promising future directions in: For qubits, the singleton gate error channels are Pauli: The amplitude damping errors for qutrits occur as idle - executing these circuit constructions experimentally " errors with the following Kraus operators: Prior Decompositions: ! = ℰ ! = %&'!' + %&)'!') + %&)!) + 1 − 3% ! to validate the error modeling & " 7 7 7 considering other common circuit patterns that 8 = ℰ 8 = 92892 + 9&89& + 9:89: - . 0 . 0 7 = 1 − 3%& ! + - %& (' ) )! ' ) could benefit from dirty qutrits constructions. 1 0 0 3 0 <& 0 0 0 <: .,0 ∈ 2,& ∖(2,2) References 0 1 − <& 0 92 = , 9& = 0 0 0 , 9: = 0 0 0 1. A. Pavlidis and E. Floratos, “Arithmetic circuits for multilevel qudits based on quantum fourier transform,” 2017. 2. Y. Fan, “Applications of multi-valued quantum algorithms,” 2008. For qutrits, we extend to generalized Pauli operators: 0 0 1 − <: 0 0 0 0 0 0 3. H. Y. Li, C. W. Wu, W. T. Liu, P. X. Chen, and C. Z. Li, “Fast quantum search algorithm for databases of arbitrary size and its implementation in a cavity QED system,” Physics Letters A, vol. 375, pp. 4249–4254, Nov. 2011. !" = ℰ ! 4. Y. Wa n g a n d M . Perkowski, “Improved complexity of quantum oracles for ternary grover algorithm for graph VTWX/YZ coloring,” in 2011 41st IEEE International Symposium on Multiple-Valued Logic, pp. 294–301, May 2011. ~N2 depth ~N depth ~lg(N) depth & with