diff --git a/check/all b/check/all
index 57fffe8223d..e8367e8dcb8 100755
--- a/check/all
+++ b/check/all
@@ -47,7 +47,7 @@ for arg in "$@"; do
     elif [[ "${arg}" == "--apply-format-changes" ]]; then
         apply_arg=( "--apply" )
     elif [[ "${#rev[@]}" == 0 ]]; then
-        if [ "$(git cat-file -t "${arg}" 2> /dev/null)" != "commit" ]; then
+        if [[ "$(git cat-file -t "${arg}" 2> /dev/null)" != "commit" ]]; then
             echo -e "\033[31mNo revision '${arg}'.\033[0m" >&2
             exit 1
         fi
@@ -61,7 +61,7 @@ done
 echo "Running misc"
 check/misc || errors+=( "check/misc failed" )
 
-if [ ${only_changed} -ne 0 ]; then
+if [[ ${only_changed} -ne 0 ]]; then
   echo "Running incremental pylint"
   check/pylint-changed-files || errors+=( "check/pylint-changed-files failed" )
 else
@@ -76,7 +76,7 @@ echo "Running incremental format"
 check/format-incremental "${rev[@]}" "${apply_arg[@]}" ||
     errors+=( "check/format-incremental failed" )
 
-if [ ${only_changed} -ne 0 ]; then
+if [[ ${only_changed} -ne 0 ]]; then
     echo "Running pytest and incremental coverage on changed files"
     check/pytest-changed-files-and-incremental-coverage "${rev[@]}" ||
          errors+=( "check/pytest-changed-files-and-incremental-coverage failed" )
diff --git a/check/format-incremental b/check/format-incremental
index d30d7c0c307..a44e98744c4 100755
--- a/check/format-incremental
+++ b/check/format-incremental
@@ -44,7 +44,7 @@ for arg in "$@"; do
         only_print=0
     elif [[ "${arg}" == "--all" ]]; then
         only_changed=0
-    elif [ -z "${rev}" ]; then
+    elif [[ -z "${rev}" ]]; then
         if ! git rev-parse --verify --quiet --no-revs "${arg}^{commit}"; then
             echo -e "\033[31mNo revision '${arg}'.\033[0m" >&2
             exit 1
@@ -59,12 +59,12 @@ done
 declare -a format_files
 if (( only_changed == 1 )); then
     # Figure out which branch to compare against.
-    if [ -z "${rev}" ]; then
-        if [ "$(git cat-file -t upstream/main 2> /dev/null)" == "commit" ]; then
+    if [[ -z "${rev}" ]]; then
+        if [[ "$(git cat-file -t upstream/main 2> /dev/null)" == "commit" ]]; then
             rev=upstream/main
-        elif [ "$(git cat-file -t origin/main 2> /dev/null)" == "commit" ]; then
+        elif [[ "$(git cat-file -t origin/main 2> /dev/null)" == "commit" ]]; then
             rev=origin/main
-        elif [ "$(git cat-file -t main 2> /dev/null)" == "commit" ]; then
+        elif [[ "$(git cat-file -t main 2> /dev/null)" == "commit" ]]; then
             rev=main
         else
             echo -e "\033[31mNo default revision found to compare against. Argument #1 must be what to diff against (e.g. 'origin/main' or 'HEAD~1').\033[0m" >&2
@@ -72,7 +72,7 @@ if (( only_changed == 1 )); then
         fi
     fi
     base="$(git merge-base "${rev}" HEAD)"
-    if [ "$(git rev-parse "${rev}")" == "${base}" ]; then
+    if [[ "$(git rev-parse "${rev}")" == "${base}" ]]; then
         echo -e "Comparing against revision '${rev}'." >&2
     else
         echo -e "Comparing against revision '${rev}' (merge base ${base})." >&2
diff --git a/check/misc b/check/misc
index 1ad4aa33378..41baaeda1f3 100755
--- a/check/misc
+++ b/check/misc
@@ -15,7 +15,7 @@ cd "${topdir}" || exit $?
 # Check for non-contrib references to contrib.
 results=$(grep -Rl "\bcirq\.contrib\b" cirq-core | grep -v "cirq/contrib" | grep -v "__")
 RESULT=$?
-if [ $RESULT -eq 0 ]; then
+if [[ $RESULT -eq 0 ]]; then
   echo -e "\033[31m'cirq.contrib' mentioned in non-contrib files:\033[0m"
   echo "${results}"
   echo
diff --git a/check/pylint-changed-files b/check/pylint-changed-files
index c88b7bcedf2..ae143beb959 100755
--- a/check/pylint-changed-files
+++ b/check/pylint-changed-files
@@ -30,17 +30,17 @@ topdir="$(git -C "${thisdir}" rev-parse --show-toplevel)" || exit $?
 cd "${topdir}" || exit $?
 
 # Figure out which revision to compare against.
-if [ -n "$1" ] && [[ $1 != -* ]]; then
+if [[ -n "$1" && $1 != -* ]]; then
     if ! git rev-parse --verify --quiet --no-revs "$1^{commit}"; then
         echo -e "\033[31mNo revision '$1'.\033[0m" >&2
         exit 1
     fi
     rev=$1
-elif [ "$(git cat-file -t upstream/main 2> /dev/null)" == "commit" ]; then
+elif [[ "$(git cat-file -t upstream/main 2> /dev/null)" == "commit" ]]; then
     rev=upstream/main
-elif [ "$(git cat-file -t origin/main 2> /dev/null)" == "commit" ]; then
+elif [[ "$(git cat-file -t origin/main 2> /dev/null)" == "commit" ]]; then
     rev=origin/main
-elif [ "$(git cat-file -t main 2> /dev/null)" == "commit" ]; then
+elif [[ "$(git cat-file -t main 2> /dev/null)" == "commit" ]]; then
     rev=main
 else
     echo -e "\033[31mNo default revision found to compare against. Argument #1 must be what to diff against (e.g. 'origin/main' or 'HEAD~1').\033[0m" >&2
@@ -65,7 +65,7 @@ declare -i num_changed=${#changed[@]}
 
 # Run it.
 echo "Found ${num_changed} lintable files associated with changes." >&2
-if [ "${num_changed}" -eq 0 ]; then
+if [[ "${num_changed}" -eq 0 ]]; then
     exit 0
 fi
 env PYTHONPATH=dev_tools pylint --jobs=0 --rcfile=dev_tools/conf/.pylintrc "${changed[@]}"
diff --git a/check/pytest b/check/pytest
index d77a28e4fc1..c4836b85c02 100755
--- a/check/pytest
+++ b/check/pytest
@@ -25,7 +25,7 @@ source dev_tools/pypath || exit $?
 pytest "${PYTEST_ARGS[@]}"
 declare -i RESULT=$?
 
-if [ "$RESULT" = 5 ]; then
+if [[ "$RESULT" = 5 ]]; then
   echo "[exit 5] No tests collected, but ignored."
   exit 0
 fi
diff --git a/check/pytest-and-incremental-coverage b/check/pytest-and-incremental-coverage
index cb348051cc5..18edcea3250 100755
--- a/check/pytest-and-incremental-coverage
+++ b/check/pytest-and-incremental-coverage
@@ -45,17 +45,17 @@ done
 
 # Figure out which revision to compare against.
 declare rev=""
-if [ -n "${baserev}" ]; then
+if [[ -n "${baserev}" ]]; then
     if ! git rev-parse --verify --quiet --no-revs "${baserev}^{commit}"; then
         echo -e "\033[31mNo revision '${baserev}'.\033[0m" >&2
         exit 1
     fi
     rev="${baserev}"
-elif [ "$(git cat-file -t upstream/main 2> /dev/null)" == "commit" ]; then
+elif [[ "$(git cat-file -t upstream/main 2> /dev/null)" == "commit" ]]; then
     rev=upstream/main
-elif [ "$(git cat-file -t origin/main 2> /dev/null)" == "commit" ]; then
+elif [[ "$(git cat-file -t origin/main 2> /dev/null)" == "commit" ]]; then
     rev=origin/main
-elif [ "$(git cat-file -t main 2> /dev/null)" == "commit" ]; then
+elif [[ "$(git cat-file -t main 2> /dev/null)" == "commit" ]]; then
     rev=main
 else
     echo -e "\033[31mNo default revision found to compare against. Argument #1 must be what to diff against (e.g. 'origin/main' or 'HEAD~1').\033[0m" >&2
diff --git a/check/pytest-changed-files b/check/pytest-changed-files
index bf289b83f4e..7a31e7160ed 100755
--- a/check/pytest-changed-files
+++ b/check/pytest-changed-files
@@ -35,18 +35,18 @@ cd "${topdir}" || exit $?
 # Figure out which branch to compare against.
 declare -a rest=( "$@" )
 declare rev=""
-if [ -n "$1" ] && [[ $1 != -* ]]; then
+if [[ -n "$1" && $1 != -* ]]; then
     if ! git rev-parse --verify --quiet --no-revs "$1^{commit}"; then
         echo -e "\033[31mNo revision '$1'.\033[0m" >&2
         exit 1
     fi
     rev=$1
     rest=( "${@:2}" )
-elif [ "$(git cat-file -t upstream/main 2> /dev/null)" == "commit" ]; then
+elif [[ "$(git cat-file -t upstream/main 2> /dev/null)" == "commit" ]]; then
     rev=upstream/main
-elif [ "$(git cat-file -t origin/main 2> /dev/null)" == "commit" ]; then
+elif [[ "$(git cat-file -t origin/main 2> /dev/null)" == "commit" ]]; then
     rev=origin/main
-elif [ "$(git cat-file -t main 2> /dev/null)" == "commit" ]; then
+elif [[ "$(git cat-file -t main 2> /dev/null)" == "commit" ]]; then
     rev=main
 else
     echo -e "\033[31mNo default revision found to compare against. Argument #1 must be what to diff against (e.g. 'origin/main' or 'HEAD~1').\033[0m" >&2
@@ -73,7 +73,7 @@ declare -i num_changed=${#changed[@]}
 
 # Run it.
 echo "Found ${num_changed} test files associated with changes." >&2
-if [ "${num_changed}" -eq 0 ]; then
+if [[ "${num_changed}" -eq 0 ]]; then
     exit 0
 fi
 
diff --git a/check/pytest-changed-files-and-incremental-coverage b/check/pytest-changed-files-and-incremental-coverage
index eb9a2ef8aaf..6e4a74d12ea 100755
--- a/check/pytest-changed-files-and-incremental-coverage
+++ b/check/pytest-changed-files-and-incremental-coverage
@@ -34,17 +34,17 @@ cd "$(git rev-parse --show-toplevel)" || exit 1
 
 # Figure out which revision to compare against.
 declare rev=""
-if [ -n "$1" ] && [[ $1 != -* ]]; then
+if [[ -n "$1" && $1 != -* ]]; then
     if ! git rev-parse --verify --quiet --no-revs "$1^{commit}"; then
         echo -e "\033[31mNo revision '$1'.\033[0m" >&2
         exit 1
     fi
     rev=$1
-elif [ "$(git cat-file -t upstream/main 2> /dev/null)" == "commit" ]; then
+elif [[ "$(git cat-file -t upstream/main 2> /dev/null)" == "commit" ]]; then
     rev=upstream/main
-elif [ "$(git cat-file -t origin/main 2> /dev/null)" == "commit" ]; then
+elif [[ "$(git cat-file -t origin/main 2> /dev/null)" == "commit" ]]; then
     rev=origin/main
-elif [ "$(git cat-file -t main 2> /dev/null)" == "commit" ]; then
+elif [[ "$(git cat-file -t main 2> /dev/null)" == "commit" ]]; then
     rev=main
 else
     echo -e "\033[31mNo default revision found to compare against. Argument #1 must be what to diff against (e.g. 'origin/main' or 'HEAD~1').\033[0m" >&2
@@ -84,7 +84,7 @@ if git diff --name-only "${rev}" -- | grep "__init__\.py$" > /dev/null; then
   # Include global API tests when an __init__ file is touched.
   changed_python_tests+=('cirq-core/cirq/protocols/json_serialization_test.py')
 fi
-if [ "${#changed_python_tests[@]}" -eq 0 ]; then
+if [[ "${#changed_python_tests[@]}" -eq 0 ]]; then
     echo -e "\033[33mNo changed files with associated python tests.\033[0m" >&2
     exit 0
 fi
diff --git a/dev_tools/packaging/produce-package.sh b/dev_tools/packaging/produce-package.sh
index 35e4f5927b6..e6b09d03d13 100755
--- a/dev_tools/packaging/produce-package.sh
+++ b/dev_tools/packaging/produce-package.sh
@@ -28,7 +28,7 @@
 set -e
 trap "{ echo -e '\033[31mFAILED\033[0m'; }" ERR
 
-if [ -z "${1}" ]; then
+if [[ -z "${1}" ]]; then
   echo -e "\033[31mNo output directory given.\033[0m"
   exit 1
 fi
@@ -49,7 +49,7 @@ repo_dir=$(git rev-parse --show-toplevel)
 cd "${repo_dir}"
 
 # Make a clean copy of HEAD, without files ignored by git (but potentially kept by setup.py).
-if [ -n "$(git status --short)" ]; then
+if [[ -n "$(git status --short)" ]]; then
     echo -e "\033[31mWARNING: You have uncommitted changes. They won't be included in the package.\033[0m"
 fi
 tmp_git_dir=$(mktemp -d "/tmp/produce-package-git.XXXXXXXXXXXXXXXX")
@@ -57,7 +57,7 @@ trap '{ rm -rf "${tmp_git_dir}"; }' EXIT
 echo "Creating pristine repository clone at ${tmp_git_dir}"
 git clone --shared --quiet "${repo_dir}" "${tmp_git_dir}"
 cd "${tmp_git_dir}"
-if [ -n "${SPECIFIED_VERSION}" ]; then
+if [[ -n "${SPECIFIED_VERSION}" ]]; then
     CURRENT_VERSION=$(set -e; my_dev_tools_modules print_version)
     my_dev_tools_modules replace_version --old="${CURRENT_VERSION}" --new="${SPECIFIED_VERSION}"
 fi
diff --git a/dev_tools/packaging/publish-dev-package.sh b/dev_tools/packaging/publish-dev-package.sh
index 2a478abb27b..21ea508da8e 100755
--- a/dev_tools/packaging/publish-dev-package.sh
+++ b/dev_tools/packaging/publish-dev-package.sh
@@ -54,7 +54,7 @@ trap "{ echo -e '\033[31mFAILED\033[0m'; }" ERR
 EXPECTED_VERSION=$1
 PROD_SWITCH=$2
 
-if [ -z "${EXPECTED_VERSION}" ]; then
+if [[ -z "${EXPECTED_VERSION}" ]]; then
     echo -e "\033[31mFirst argument must be the expected version.\033[0m"
     exit 1
 fi
@@ -63,34 +63,34 @@ if [[ "${EXPECTED_VERSION}" != *dev* ]]; then
   exit 1
 fi
 ACTUAL_VERSION_LINE=$(tail -n 1 "${PROJECT_NAME}/_version.py")
-if [ "${ACTUAL_VERSION_LINE}" != '__version__ = "'"${EXPECTED_VERSION}"'"' ]; then
+if [[ "${ACTUAL_VERSION_LINE}" != '__version__ = "'"${EXPECTED_VERSION}"'"' ]]; then
   echo -e "\033[31mExpected version (${EXPECTED_VERSION}) didn't match the one in ${PROJECT_NAME}/_version.py (${ACTUAL_VERSION_LINE}).\033[0m"
   exit 1
 fi
 
-if [ -z "${PROD_SWITCH}" ] || [ "${PROD_SWITCH}" = "--test" ]; then
+if [[ -z "${PROD_SWITCH}" || "${PROD_SWITCH}" = "--test" ]]; then
     PYPI_REPOSITORY_FLAG=( "--repository-url=https://test.pypi.org/legacy/" )
     PYPI_REPO_NAME="TEST"
     USERNAME="${TEST_TWINE_USERNAME}"
     PASSWORD="${TEST_TWINE_PASSWORD}"
-    if [ -z "${USERNAME}" ]; then
+    if [[ -z "${USERNAME}" ]]; then
       echo -e "\033[31mTEST_TWINE_USERNAME environment variable must be set.\033[0m"
       exit 1
     fi
-    if [ -z "${PASSWORD}" ]; then
+    if [[ -z "${PASSWORD}" ]]; then
       echo -e "\033[31mTEST_TWINE_PASSWORD environment variable must be set.\033[0m"
       exit 1
     fi
-elif [ "${PROD_SWITCH}" = "--prod" ]; then
+elif [[ "${PROD_SWITCH}" = "--prod" ]]; then
     PYPI_REPOSITORY_FLAG=( )
     PYPI_REPO_NAME="PROD"
     USERNAME="${PROD_TWINE_USERNAME}"
     PASSWORD="${PROD_TWINE_PASSWORD}"
-    if [ -z "${USERNAME}" ]; then
+    if [[ -z "${USERNAME}" ]]; then
       echo -e "\033[31mPROD_TWINE_USERNAME environment variable must be set.\033[0m"
       exit 1
     fi
-    if [ -z "${PASSWORD}" ]; then
+    if [[ -z "${PASSWORD}" ]]; then
       echo -e "\033[31mPROD_TWINE_PASSWORD environment variable must be set.\033[0m"
       exit 1
     fi
diff --git a/dev_tools/packaging/verify-published-package.sh b/dev_tools/packaging/verify-published-package.sh
index db3f9b3b31d..694b273a602 100755
--- a/dev_tools/packaging/verify-published-package.sh
+++ b/dev_tools/packaging/verify-published-package.sh
@@ -37,18 +37,18 @@ PROJECT_NAME=cirq
 PROJECT_VERSION=$1
 PROD_SWITCH=$2
 
-if [ -z "${PROJECT_VERSION}" ]; then
+if [[ -z "${PROJECT_VERSION}" ]]; then
     echo -e "\033[31mFirst argument must be the package version to test.\033[0m"
     exit 1
 fi
 
 declare -a PIP_FLAGS
 
-if [ "${PROD_SWITCH}" = "--test" ]; then
+if [[ "${PROD_SWITCH}" = "--test" ]]; then
     PIP_FLAGS=("--index-url=https://test.pypi.org/simple/")
     PYPI_REPO_NAME="TEST"
     PYPI_PROJECT_NAME="cirq"
-elif [ "${PROD_SWITCH}" = "--prod" ]; then
+elif [[ "${PROD_SWITCH}" = "--prod" ]]; then
     PIP_FLAGS=()
     PYPI_REPO_NAME="PROD"
     PYPI_PROJECT_NAME="cirq"
@@ -67,7 +67,7 @@ cd "${tmp_dir}"
 trap '{ rm -rf "${tmp_dir}"; }' EXIT
 
 # Test installation from published package
-PYTHON_VERSION=python3
+                            PYTHON_VERSION=python3
 
 # Prepare.
 CONTRIB_DEPS_FILE="${REPO_ROOT}/cirq-core/cirq/contrib/requirements.txt"