diff --git a/jaxquantum/core/conversions.py b/jaxquantum/core/conversions.py
index 131ef99..ac7eb2c 100644
--- a/jaxquantum/core/conversions.py
+++ b/jaxquantum/core/conversions.py
@@ -2,9 +2,10 @@
 Converting between different object types.
 """
 
+from numbers import Number
 from jax import config, Array
 from qutip import Qobj
-from typing import Optional
+from typing import Optional, Union, List
 import jax.numpy as jnp
 import numpy as np
 
@@ -46,15 +47,37 @@ def jqt2qt(jqt_obj):
     
     return Qobj(np.array(jqt_obj.data), dims=jqt_obj.dims)
 
-def jnp2jqt(arr: Array, dims: Optional[DIMS_TYPE] = None):
+
+def extract_dims(arr: Array, dims: Optional[Union[DIMS_TYPE, List[int]]] = None):
+    """Extract dims from a JAX array or Qarray.
+
+    Args:
+        arr: JAX array or Qarray.
+        dims: Qarray dims.
+
+    Returns:
+        Qarray dims.
+    """
+    if isinstance(dims[0], Number):
+        is_op = len(arr.shape) == 2 and arr.shape[0] == arr.shape[1]
+        if is_op:
+            dims = [dims, dims]
+        else:
+            dims = [dims, [1] * len(dims)] # defaults to ket 
+    return dims
+                 
+
+def jnp2jqt(arr: Array, dims: Optional[Union[DIMS_TYPE, List[int]]] = None):
     """JAX array -> QuTiP state.
 
     Args:
         jnp_obj: JAX array.
+        dims: Qarray dims.
 
     Returns:
         QuTiP state.
     """
+    dims = extract_dims(arr, dims)
     return Qarray.create(arr, dims=dims)
 
 
@@ -67,6 +90,8 @@ def jnps2jqts(arrs: Array, dims: Optional[DIMS_TYPE] = None):
     Returns:
         QuTiP state.
     """
+
+    dims = extract_dims(arrs[0], dims)
     return [Qarray.create(arr, dims=dims) for arr in arrs]
 
 def jqts2jnps(qarrs: Qarray):
diff --git a/jaxquantum/core/qarray.py b/jaxquantum/core/qarray.py
index 96f119d..536b496 100644
--- a/jaxquantum/core/qarray.py
+++ b/jaxquantum/core/qarray.py
@@ -239,6 +239,9 @@ def dims(self):
     def data(self):
         return self._data
     
+    @property
+    def shaped_data(self):
+        return self._data.reshape(self.dims[0] + self.dims[1])
 
     def _str_header(self):
         out = ", ".join([
@@ -334,7 +337,7 @@ def tensor(*args, **kwargs) -> Qarray:
         dims[1] += arg.dims[1]
     return Qarray.create(data, dims=dims)
 
-def tr(qarr: Qarray, **kwargs) -> Qarray:
+def tr(qarr: Qarray, **kwargs) -> jnp.complex128:
     """Full trace.
 
     Args:
@@ -343,7 +346,7 @@ def tr(qarr: Qarray, **kwargs) -> Qarray:
     Returns:
         Full trace.
     """
-    return jnp.trace(qarr.data, **kwargs)
+    return trace(qarr, **kwargs)
 
 
 def expm_data(data: Array, **kwargs) -> Array:
@@ -425,13 +428,10 @@ def ptrace(qarr: Qarray, indx) -> Qarray:
     """
 
     qarr = ket2dm(qarr)
-    rho = qarr.data
+    rho = qarr.shaped_data
     dims = qarr.dims
 
     Nq = len(dims[0])
-    dims2 = jnp.concatenate(jnp.array(dims))
-
-    rho = rho.reshape(dims2)
 
     indxs = [indx, indx + Nq]
     for j in range(Nq):
@@ -446,6 +446,9 @@ def ptrace(qarr: Qarray, indx) -> Qarray:
 
     return Qarray.create(rho)
 
+def trace(qarr: Qarray, **kwargs) -> Qarray:
+    return jnp.trace(qarr.data, **kwargs)
+
 def dag(qarr: Qarray) -> Qarray:
     """Conjugate transpose.