Experimental demonstration of work fluctuations along a shortcut to adiabaticity with a superconducting Xmon qubit

  1. Zhenxing Zhang,
  2. Tenghui Wang,
  3. Liang Xiang,
  4. Zhilong Jia,
  5. Peng Duan,
  6. Weizhou Cai,
  7. Ze Zhan,
  8. Zhiwen Zong,
  9. Jianlan Wu,
  10. Luyan Sun,
  11. Yi Yin,
  12. and Guoping Guo
In a `shortcut-to-adiabaticity‘ (STA) protocol, the counter-diabatic Hamiltonian, which suppresses the non-adiabatic transition of a reference `adiabatic‘ trajectory, induces
a quantum uncertainty of the work cost in the framework of quantum thermodynamics. Following a theory derived recently [Funo et al 2017 Phys. Rev. Lett. 118 100602], we perform an experimental measurement of the STA work statistics in a high-quality superconducting Xmon qubit. Through the frozen-Hamiltonian and frozen-population techniques, we experimentally realize the two-point measurement of the work distribution for given initial eigenstates. Our experimental statistics verify (i) the conservation of the average STA work and (ii) the equality between the STA excess of work fluctuations and the quantum geometric tensor.

Simulating a Topological Transition in a Superconducting Phase Qubit by Fast Adiabatic Trajectories

  1. Tenghui Wang,
  2. Zhenxing Zhang,
  3. Liang Xiang,
  4. Zhihao Gong,
  5. Jianlan Wu,
  6. and Yi Yin
The significance of topological phases has been widely recognized in the community of condensed matter physics. The well controllable quantum systems provide an artificial platform
to probe and engineer various topological phases. The adiabatic trajectory of a quantum state describes the change of the bulk Bloch eigenstates with the momentum, and this adiabatic simulation method is however practically limited due to quantum dissipation. Here we apply the `shortcut to adiabaticity‘ (STA) protocol to realize fast adiabatic evolutions in the system of a superconducting phase qubit. The resulting fast adiabatic trajectories illustrate the change of the bulk Bloch eigenstates in the Su-Schrieffer-Heeger (SSH) model. A sharp transition is experimentally determined for the topological invariant of a winding number. Our experiment helps identify the topological Chern number of a two-dimensional toy model, suggesting the applicability of the fast adiabatic simulation method for topological systems.

Measuring the Berry Phase in a Superconducting Phase Qubit by a Shortcut to Adiabaticity

  1. Zhenxing Zhang,
  2. Tenghui Wang,
  3. Liang Xiang,
  4. Jiadong Yao,
  5. Jianlan Wu,
  6. and Yi Yin
With a counter-diabatic field supplemented to the reference control field, the `shortcut to adiabaticiy‘ (STA) protocol is implemented in a superconducting phase qubit. The Berry
phase measured in a short time scale is in good agreement with the theoretical result acquired from an adiabatic loop. The trajectory of a qubit vector is extracted, verifying the Berry phase alternatively by the integrated solid angle. The classical noise is introduced to the amplitude or phase of the total control field. In the statistics of the Berry phase, the mean with either noise is almost equal to that without noise, while the variation with the amplitude noise can be described by an analytical expression.

Simulating weak localization using superconducting quantum circuits

  1. Yu Chen,
  2. P. Roushan,
  3. D. Sank,
  4. C. Neill,
  5. Erik Lucero,
  6. Matteo Mariantoni,
  7. R. Barends,
  8. B. Chiaro,
  9. J. Kelly,
  10. A. Megrant,
  11. J. Y. Mutus,
  12. P. J. J. O'Malley,
  13. A. Vainsencher,
  14. J. Wenner,
  15. T. C. White,
  16. Yi Yin,
  17. A. N. Cleland,
  18. and John M. Martinis
Understanding complex quantum matter presents a central challenge in condensed matter physics. The difficulty lies in the exponential scaling of the Hilbert space with the system size,
making solutions intractable for both analytical and conventional numerical methods. As originally envisioned by Richard Feynman, this class of problems can be tackled using controllable quantum simulators. Despite many efforts, building an quantum emulator capable of solving generic quantum problems remains an outstanding challenge, as this involves controlling a large number of quantum elements. Here, employing a multi-element superconducting quantum circuit and manipulating a single microwave photon, we demonstrate that we can simulate the weak localization phenomenon observed in mesoscopic systems. By engineering the control sequence in our emulator circuit, we are also able to reproduce the well-known temperature dependence of weak localization. Furthermore, we can use our circuit to continuously tune the level of disorder, a parameter that is not readily accessible in mesoscopic systems. By demonstrating a high level of control and complexity, our experiment shows the potential for superconducting quantum circuits to realize scalable quantum simulators.

Catching Shaped Microwave Photons with 99.4% Absorption Efficiency

  1. J. Wenner,
  2. Yi Yin,
  3. Yu Chen,
  4. R. Barends,
  5. B. Chiaro,
  6. E. Jeffrey,
  7. J. Kelly,
  8. A. Megrant,
  9. J. Y. Mutus,
  10. C. Neill,
  11. P. J. J. O'Malley,
  12. P. Roushan,
  13. D. Sank,
  14. A. Vainsencher,
  15. T. C. White,
  16. Alexander N. Korotkov,
  17. A. N. Cleland,
  18. and John M. Martinis
Quantum information systems require high fidelity quantum operations. It is particularly challenging to convert flying qubits to stationary qubits for deterministic quantum networks,
since absorbing naturally shaped emission has a maximum fidelity of only 54%. Theoretical protocols reaching 100% efficiency rely upon sculpting the time dependence of photon wavepackets and receiver coupling. Using these schemes, experimental fidelities have reached up to 20% for optical photons and 81% for microwave photons, although with drive pulses much longer than the cavity decay rate. Here, we demonstrate a particularly simple „time reversed“ photon shape and gated receiver with an absorption fidelity of 99.4% and a receiver efficiency of 97.4% for microwave photons. We classically drive a superconducting coplanar waveguide resonator an order of magnitude shorter than the intrinsic decay time. With the fidelity now at the error threshold for fault tolerant quantum communication (96%) and computation (99.4%) and comparable to fidelities of good logic gates and measurements, new designs may be envisioned for quantum communication and computation systems.

Sputtered TiN films for superconducting coplanar waveguide resonators

  1. Shinobu Ohya,
  2. Ben Chiaro,
  3. Anthony Megrant,
  4. Charles Neill,
  5. Rami Barends,
  6. Yu Chen,
  7. Julian Kelly,
  8. David Low,
  9. Josh Mutus,
  10. Peter O'Malley,
  11. Pedram Roushan,
  12. Daniel Sank,
  13. Amit Vainsencher,
  14. James Wenner,
  15. Theodore C. White,
  16. Yi Yin,
  17. B. D. Schultz,
  18. Chris J Palmstrøm,
  19. Benjamin A. Mazin,
  20. Andrew N. Cleland,
  21. and John M. Martinis
We present a systematic study of the properties of TiN films by varying the deposition conditions in an ultra-high-vacuum reactive magnetron sputtering chamber. By increasing the deposition
pressure from 2 to 9 mTorr while keeping a nearly stoichiometric composition of Ti(1-x)N(x) (x=0.5), the film resistivity increases, the dominant crystal orientation changes from (100) to (111), grain boundaries become clearer, and the strong compressive strain changes to weak tensile strain. The TiN films absorb a high concentration of contaminants including hydrogen, carbon, and oxygen when they are exposed to air after deposition. With the target-substrate distance set to 88 mm the contaminant levels increase from ~0.1% to ~10% as the pressure is increased from 2 to 9 mTorr. The contaminant concentrations also correlate with in-plane distance from the center of the substrate and increase by roughly two orders of magnitude as the target-substrate distance is increased from 88 mm to 266 mm. These contaminants are found to strongly influence the properties of TiN films. For instance, the resistivity of stoichiometric films increases by around a factor of 5 as the oxygen content increases from 0.1% to 11%. These results suggest that the sputtered TiN particle energy is critical in determining the TiN film properties, and that it is important to control this energy to obtain high-quality TiN films. Superconducting coplanar waveguide resonators made from a series of nearly stoichiometric films grown at pressures from 2 mTorr to 7 mTorr show an increase in intrinsic quality factor from ~10^4 to ~10^6 as the magnitude of the compressive strain decreases from nearly 3800 MPa to approximately 150 MPa and the oxygen content increases from 0.1% to 8%. The films with a higher oxygen content exhibit lower loss, but the nonuniformity of the oxygen incorporation hinders the use of sputtered TiN in larger circuits.

Multiplexed dispersive readout of superconducting phase qubits

  1. Yu Chen,
  2. D. Sank,
  3. P. O'Malley,
  4. T. White,
  5. R. Barends,
  6. B. Chiaro,
  7. J. Kelly,
  8. E. Lucero,
  9. M. Mariantoni,
  10. A. Megrant,
  11. C. Neill,
  12. A. Vainsencher,
  13. J. Wenner,
  14. Yi Yin,
  15. A. N. Cleland,
  16. and John M. Martinis
We introduce a frequency-multiplexed readout scheme for superconducting phase qubits. Using a quantum circuit with four phase qubits, we couple each qubit to a separate lumped-element
superconducting readout resonator, with the readout resonators connected in parallel to a single measurement line. The readout resonators and control electronics are designed so that all four qubits can be read out simultaneously using frequency multiplexing on the one measurement line. This technology provides a highly efficient and compact means for reading out multiple qubits, a significant advantage for scaling up to larger numbers of qubits.

Excitation of superconducting qubits from hot non-equilibrium quasiparticles

  1. J. Wenner,
  2. Yi Yin,
  3. Erik Lucero,
  4. R. Barends,
  5. Yu Chen,
  6. B. Chiaro,
  7. J. Kelly,
  8. M. Lenander,
  9. Matteo Mariantoni,
  10. A. Megrant,
  11. C. Neill,
  12. P. J. J. O'Malley,
  13. D. Sank,
  14. A. Vainsencher,
  15. H. Wang,
  16. T. C. White,
  17. A. N. Cleland,
  18. and John M. Martinis
Superconducting qubits probe environmental defects such as non-equilibrium quasiparticles, an important source of decoherence. We show that „hot“ non-equilibrium quasiparticles,
with energies above the superconducting gap, affect qubits differently from quasiparticles at the gap, implying qubits can probe the dynamic quasiparticle energy distribution. For hot quasiparticles, we predict a non-neligable increase in the qubit excited state probability P_e. By injecting hot quasiparticles into a qubit, we experimentally measure an increase of P_e in semi-quantitative agreement with the model.

Controlled catch and release of microwave photon states

  1. Yi Yin,
  2. Yu Chen,
  3. Daniel Sank,
  4. P. J. J. O'Malley,
  5. T. C. White,
  6. R. Barends,
  7. J. Kelly,
  8. Erik Lucero,
  9. Matteo Mariantoni,
  10. A. Megrant,
  11. C. Neill,
  12. A. Vainsencher,
  13. J. Wenner,
  14. Alexander N. Korotkov,
  15. A. N. Cleland,
  16. and John M. Martinis
, in which the resonant cavity confines photons and promotes"]strong light-matter interactions. The cavity end-mirrors determine the performance of the coupled system, with higher mirror reflectivity yielding better quantum coherence, but higher mirror transparency giving improved measurement and control, forcing a compromise. An alternative is to control the mirror transparency, enabling switching between long photon lifetime during quantum interactions and large signal strength when performing measurements. Here we demonstrate the superconducting analogue, using a quantum system comprising a resonator and a qubit, with variable coupling to a measurement transmission line. The coupling can be adjusted through zero to a photon emission rate 1,000 times the intrinsic photon decay rate. We use this system to control photons in coherent states as well as in non-classical Fock states, and dynamically shape the waveform of released photons. This has direct applications to circuit quantum electrodynamics [3], and may enable high-fidelity quantum state transfer between distant qubits, for which precisely-controlled waveform shaping is a critical and non-trivial requirement [4, 5].

Computing prime factors with a Josephson phase qubit quantum processor

  1. Erik Lucero,
  2. Rami Barends,
  3. Yu Chen,
  4. Julian Kelly,
  5. Matteo Mariantoni,
  6. Anthony Megrant,
  7. Peter O'Malley,
  8. Daniel Sank,
  9. Amit Vainsencher,
  10. James Wenner,
  11. Ted White,
  12. Yi Yin,
  13. Andrew N. Cleland,
  14. and John M. Martinis
. Compiled versions of Shor’s algorithm have been demonstrated"]on ensemble quantum systems[2] and photonic systems[3-5], however this has yet to be shown using solid state quantum bits (qubits). Two advantages of superconducting qubit architectures are the use of conventional microfabrication techniques, which allow straightforward scaling to large numbers of qubits, and a toolkit of circuit elements that can be used to engineer a variety of qubit types and interactions[6, 7]. Using a number of recent qubit control and hardware advances [7-13], here we demonstrate a nine-quantum-element solid-state QuP and show three experiments to highlight its capabilities. We begin by characterizing the device with spectroscopy. Next, we produces coherent interactions between five qubits and verify bi- and tripartite entanglement via quantum state tomography (QST) [8, 12, 14, 15]. In the final experiment, we run a three-qubit compiled version of Shor’s algorithm to factor the number 15, and successfully find the prime factors 48% of the time. Improvements in the superconducting qubit coherence times and more complex circuits should provide the resources necessary to factor larger composite numbers and run more intricate quantum algorithms.