专利汇可以提供Hybrid quantum circuit assembly专利检索,专利查询,专利分析的服务。并且Systems and methods are provided for a hybrid qubit circuit assembly is provided. A first plural set of Josephson junctions is arranged in series on a first path between two nodes of a circuit. A second plural set of Josephson junctions is arranged in parallel with one another to form a direct current superconducting quantum interference device (DC SQUID). The DC SQUID is in parallel with the first plural set of Josephson junctions. A capacitor is in parallel with each of the first plural set of Josephson junctions and the DC SQUID.,下面是Hybrid quantum circuit assembly专利的具体信息内容。
Having described the invention, we claim:
This application relates generally to quantum computers, and more specifically, to a hybrid quantum circuit assembly.
A classical computer operates by processing binary bits of information that change state according to the laws of classical physics. These information bits can be modified by using simple logic gates such as AND and OR gates. The binary bits are physically created by a high or a low energy level occurring at the output of the logic gate to represent either a logical one (e.g. high voltage) or a logical zero (e.g. low voltage). A classical algorithm, such as one that multiplies two integers, can be decomposed into a long string of these simple logic gates. Like a classical computer, a quantum computer also has bits and gates. Instead of using logical ones and zeroes, a quantum bit (“qubit”) uses quantum mechanics to occupy both possibilities simultaneously. This ability means that a quantum computer can solve certain problems with exponentially greater efficiency than that of a classical computer.
In accordance with one example, a hybrid qubit circuit assembly is provided. A first plural set of Josephson junctions is arranged in series on a first path between two nodes of a circuit. A second plural set of Josephson junctions is arranged in parallel with one another to form a direct current superconducting quantum interference device (DC SQUID). The DC SQUID is in parallel with the first plural set of Josephson junctions. A capacitor is in parallel with each of the first plural set of Josephson junctions and the DC SQUID.
In accordance with another example, a method is provided for preparing a hybrid qubit circuit assembly in an arbitrary state. The method includes adiabatically transitioning the hybrid qubit from a Transmon regime to a flux regime via a first control flux, and rapidly transitioning a second control flux at a sweep rate through a hybridization gap associated with the flux regime. The hybrid qubit is then adiabatically transitioned from a flux regime to a Transmon regime via a first control flux.
In accordance with yet another example, a method is provided for performing a single qubit rotation with a hybrid qubit circuit assembly. The hybrid qubit is rapidly transitioned from a Transmon regime to a flux regime via a classical control, and maintained in the flux regime for a time period having a duration that is a function of a desired magnitude of the rotation. The hybrid qubit is then rapidly transitioned from the flux regime back to the Transmon regime via the classical control.
The features, objects, and advantages of the hybrid qubit assembly will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, wherein:
A hybrid quantum circuit assembly is capable of operating as either a flux qubit or a Transmon qubit. The circuit can be transitioned between these two functions, or operating regimes, by adjusting a classical control, such as a current driver inductively coupled to the qubit circuit assembly to provide a control flux to the circuit. The term “classical” implies that the manner of control behaves generally according to the laws of classical physics. In addition to selectively providing the advantages of both flux and Transmon qubit, the proposed assembly can be switched between the flux qubit and the Transmon qubit regimes to perform various quantum operations, including arbitrary quantum rotations.
The Transmon qubit is considered to be one of the most promising devices for a scalable quantum computing architecture because of its long coherence time. The Transmon qubit operates within a so-called circuit QED architecture, where the qubit is coupled strongly to a high Q resonator that functions simultaneously as a coupling bus, a filter, and a readout device. Unfortunately, existing Transmon qubits generally require microwave pulses to realize single-qubit gates. Flux qubits can be readily used for read-out and state preparation, but lack the long coherence time of the Transmon. The hybrid quantum circuit assembly described herein allows the Transmon qubit to realize single qubit gates, state preparation, and readout without the need for microwave pulses, and this capability opens the way to large scale integration of these hybrid qubits with local, on chip digital control circuitry.
The hybrid quantum circuit assembly 10 is configured to transition from a flux qubit regime to a Transmon qubit regime based on a first control flux, Φα, provided by a first classical control 24 to the DC SQUID 20. In one example, the first classical control 24 can be implemented as a reciprocal quantum logic (RQL) driver providing a control current to a loop inductively coupled to the DC SQUID 20. The first control flux, Φα, controls the effective critical current of the dc SQUID, such that the effective critical current, Ic, can be expressed as:
Ic=2Ic1∥cos(πΦα/Φ0)| Eq. 1
where Ic1 is a critical current of each the Josephson junctions 16 and 18 comprising the DC SQUID 20, and Φ0 is the magnetic flux quantum, approximately equal to 2.068×10−15 Webers.
When Φα is tuned such that the critical current of the DC SQUID 20 is greater than half the critical current of the first plural set of Josephson junctions 12 and 14, that is, Ic>0.5*Ic2,3, the qubit behaves as a flux qubit, and its basis states are the left- and right-circulating persistent current states |L and |R. When the critical current is at this level, the potential energy of the qubit has a double-well form, with a barrier of raised energy separating the two potential wells containing the left- and right-circulating persistent current states. As Ic is reduced, the height of the barrier between the left and right wells is also reduced and the |L and |R states hybridize as would be expected in a flux qubit. When the critical current of the dc SQUID is reduced further by the control flux, Φα, the barrier between the wells vanishes and the qubit potential becomes a single well, nonlinear oscillator. At this point, the hybrid quantum circuit assembly 10 functions as a Transmon qubit.
The hybrid quantum circuit assembly 10 uses the tunability of the potential energy barrier to move the qubit between fundamentally different operating regimes, providing a number of advantages. For example, the Transmon operating regime of the qubit can be used as a starting point for a given quantum operation, and the flux-qubit like regime can be accessed via control flux Φα to perform single qubit rotations, state preparation, and readout. Methods for performing these functions are described in detail below in
A system control 126 is operatively connected to a first classical control 130 and a second classical control 140, such that the system control can control respective magnitudes of the first and second control fluxes. The system control 126 can be implemented, for example, as dedicated hardware, software or firmware executed on a general purpose computer, or some combination of software and dedicated hardware. The first classical control 130 is configured to control a depth of the potential energy wells, or rather, the height of the barrier separating them, associated with the |L and |R states by providing a first control flux, Φα, to the DC SQUID 120. The barrier between the states can be tuned to a negligible height to allow the system to operate as a Transmon qubit. The first classical control 130 includes a first RQL driver 132 and a first current loop 134 inductively coupled to the DC SQUID 120. The second classical control 140 is configured to control the symmetry of the qubit potential by providing a second control flux, ΦΔ, to the circuit. The second classical control 140 includes a first RQL driver 142 and a current loop 144 inductively coupled to the hybrid quantum circuit assembly 110.
For Φα>0.5 Φ0, the energy degeneracy of |L and |R occurs at ΦΔ=0, and for Φα<0.5 Φ0, the energy degeneracy of |L and |R occurs at ΦΔ=0.5. For Φα<0.58 Φ0, the energy levels become nearly independent of ΦΔ. This regime corresponds to the qubit potential having the form of
At one end of the superconductive film 182, first and second Josephson junctions 186 and 188 are provided in parallel to either side of the first superconductive film 182 to form a DC SQUID. Third and fourth Josephson junctions 190 and 192 are arranged collinearly with a midline of the first superconductive film 182. The superconductive film 182 forms an interdigitated capacitor 194 between superconducting film 182 and ground plane 184. The first control flux, Φα, is applied in the common mode of the loop defined by borders of the ground plane and junctions 186 and 188. The second control flux, ΦΔ, is applied to one of the loops formed by a trace containing the third and fourth Josephson junctions 190 and 192. In this implementation, a positive adjustment to the flux, relative to the symmetry point, is provided by applying the flux to one loop, and a negative flux is provided by providing the flux to the other loop. This arrangement ensures that the two control fluxes can be applied independently from each other with minimal cross-talk.
Throughout the foregoing disclosure, various methods for creating quantum logic gates are implied. The following embodiments are provided to expressly illustrate methods for implementing quantum logic operations with the hybrid qubit assembly. These methods may be embodied, in whole or in part, as processing steps stored in a classical computer memory and executable by a classical computer processor for manipulating a hybrid quantum circuit.
At 208, the second control flux is adjusted nonadibatically, such that the qubit is swept through the hybridization gap at δΦΔ=0, where both the |L and |R states become populated due to Landau-Zener tunneling with weights that depend on the ratio of the sweep rate to the gap energy. This operation is denoted as (3) in
Prior to beginning the method 300, the qubit is in the Transmon regime. A value for the second control flux can be selected according to a desired axis of the single qubit rotation, and the second control flux can be tuned to that value, represented in
The invention has been disclosed illustratively. Accordingly, the terminology employed throughout the disclosure should be read in an exemplary rather than a limiting manner. Although minor modifications of the invention will occur to those well versed in the art, it shall be understood that what is intended to be circumscribed within the scope of the patent warranted hereon are all such embodiments that reasonably fall within the scope of the advancement to the art hereby contributed, and that that scope shall not be restricted.
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