Srikanth Srinivasan
Indian Institute of Technology Bombay
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Featured researches published by Srikanth Srinivasan.
Nature Communications | 2015
Antonio Corcoles; Easwar Magesan; Srikanth Srinivasan; Andrew W. Cross; Matthias Steffen; Jay Gambetta; Jerry M. Chow
To build a fault-tolerant quantum computer, it is necessary to implement a quantum error correcting code. Such codes rely on the ability to extract information about the quantum error syndrome while not destroying the quantum information encoded in the system. Stabilizer codes are attractive solutions to this problem, as they are analogous to classical linear codes, have simple and easily computed encoding networks, and allow efficient syndrome extraction. In these codes, syndrome extraction is performed via multi-qubit stabilizer measurements, which are bit and phase parity checks up to local operations. Previously, stabilizer codes have been realized in nuclei, trapped-ions, and superconducting qubits. However these implementations lack the ability to perform fault-tolerant syndrome extraction which continues to be a challenge for all physical quantum computing systems. Here we experimentally demonstrate a key step towards this problem by using a twoby-two lattice of superconducting qubits to perform syndrome extraction and arbitrary error detection via simultaneous quantum non-demolition stabilizer measurements. This lattice represents a primitive tile for the surface code (SC), which is a promising stabilizer code for scalable quantum computing. Furthermore, we successfully show the preservation of an entangled state in the presence of an arbitrary applied error through high-fidelity syndrome measurement. Our results bolster the promise of employing lattices of superconducting qubits for larger-scale fault-tolerant quantum computing.The ability to detect and deal with errors when manipulating quantum systems is a fundamental requirement for fault-tolerant quantum computing. Unlike classical bits that are subject to only digital bit-flip errors, quantum bits are susceptible to a much larger spectrum of errors, for which any complete quantum error-correcting code must account. Whilst classical bit-flip detection can be realized via a linear array of qubits, a general fault-tolerant quantum error-correcting code requires extending into a higher-dimensional lattice. Here we present a quantum error detection protocol on a two-by-two planar lattice of superconducting qubits. The protocol detects an arbitrary quantum error on an encoded two-qubit entangled state via quantum non-demolition parity measurements on another pair of error syndrome qubits. This result represents a building block towards larger lattices amenable to fault-tolerant quantum error correction architectures such as the surface code.
Nature Communications | 2014
Jerry M. Chow; Jay Gambetta; Easwar Magesan; David W. Abraham; Andrew W. Cross; Blake Johnson; Nicholas Masluk; Colm A. Ryan; John A. Smolin; Srikanth Srinivasan; Matthias Steffen
With favourable error thresholds and requiring only nearest-neighbour interactions on a lattice, the surface code is an error-correcting code that has garnered considerable attention. At the heart of this code is the ability to perform a low-weight parity measurement of local code qubits. Here we demonstrate high-fidelity parity detection of two code qubits via measurement of a third syndrome qubit. With high-fidelity gates, we generate entanglement distributed across three superconducting qubits in a lattice where each code qubit is coupled to two bus resonators. Via high-fidelity measurement of the syndrome qubit, we deterministically entangle the code qubits in either an even or odd parity Bell state, conditioned on the syndrome qubit state. Finally, to fully characterize this parity readout, we develop a measurement tomography protocol. The lattice presented naturally extends to larger networks of qubits, outlining a path towards fault-tolerant quantum computing.
Physical Review Letters | 2011
Anthony J. Hoffman; Srikanth Srinivasan; Sebastian Schmidt; Lafe Spietz; Jose Aumentado; Hakan E. Türeci; Andrew Houck
Mediated photon-photon interactions are realized in a superconducting coplanar waveguide cavity coupled to a superconducting charge qubit. These nonresonant interactions blockade the transmission of photons through the cavity. This so-called dispersive photon blockade is characterized by measuring the total transmitted power while varying the energy spectrum of the photons incident on the cavity. A staircase with four distinct steps is observed and can be understood in an analogy with electron transport and the Coulomb blockade in quantum dots. This work differs from previous efforts in that the cavity-qubit excitations retain a photonic nature rather than a hybridization of qubit and photon and provides the needed tolerance to disorder for future condensed matter experiments.
Physical Review Letters | 2011
Srikanth Srinivasan; Anthony J. Hoffman; Jay M. Gambetta; Andrew Houck
Recent progress in superconducting qubits has demonstrated the potential of these devices for the future of quantum information processing. One desirable feature for quantum computing is independent control of qubit interactions as well as qubit energies. We demonstrate a new type of superconducting charge qubit that has a Vshaped energy spectrum and uses quantum interference to provide independent control over the qubit energy and dipole coupling to a superconducting cavity. We demonstrate dynamic access to the strong coupling regime by tuning the coupling strength from less than 200 kHz to more than 40 MHz. This tunable coupling can be used to protect the qubit from cavity-induced relaxation and avoid unwanted qubit-qubit interactions in a multi-qubit system.
foundations of computer science | 2014
Neeraj Kayal; Nutan Limaye; Chandan Saha; Srikanth Srinivasan
We show here a 2<sup>Ω(√d·log N)</sup> size lower bound for homogeneous depth four arithmetic formulas. That is, we give an explicit family of polynomials of degree d on N variables (with N = d<sup>3</sup> in our case) with 0, 1-coefficients such that for any representation of a polynomial f in this family of the form f = Σ<sub>i</sub> Π<sub>j</sub> Q<sub>ij</sub>, where the Qijs are homogeneous polynomials (recall that a polynomial is said to be homogeneous if all its monomials have the same degree), it must hold that Σi,j (Number of monomials of Q<sub>ij</sub>) ≥ 2<sup>Ω(√d·log N)</sup>. The above mentioned family, which we refer to as the NisanWigderson design-based family of polynomials, is in the complexity class VNP. Our work builds on the recent lower bound results [1], [2], [3], [4], [5] and yields an improved quantitative bound as compared to the quasi-polynomial lower bound of [6] and the N<sup>Ω(log log N)</sup> lower bound in the independent work of [7].
foundations of software technology and theoretical computer science | 2009
Vikraman Arvind; Pushkar S. Joglekar; Srikanth Srinivasan
Motivated by the Hadamard product of matrices we define the Hadamard product of multivariate polynomials and study its arithmetic circuit and branching program complexity. We also give applications and connections to polynomial identity testing. Our main results are the following. 1. We show that noncommutative polynomial identity testing for algebraic branching programs over rationals is complete for the logspace counting class
Physical Review A | 2014
Srikanth Srinivasan; Neereja Sundaresan; Darius Sadri; Yanbing Liu; Jay Gambetta; Terri Yu; S. M. Girvin; Andrew Houck
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Combinatorica | 2016
Justin Gilmer; Michael E. Saks; Srikanth Srinivasan
, and over fields of characteristic
international colloquium on automata languages and programming | 2012
Rahul Santhanam; Srikanth Srinivasan
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Physical Review B | 2011
Anthony J. Hoffman; Srikanth Srinivasan; Jay Gambetta; Andrew Houck
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